Water heater and water heater component construction

ABSTRACT

A water jacket assembly for an instantaneous gas fired water heater, the assembly including pressed profiled plates made of copper or copper coated steel, one plate being the inverted image of the other, said plates being placed together in pairs, the pairs of plates being arranged in a parallel array to form a heat exchanger, the heat exchanger being bordered by a water jacket comprising overlapping side and end panels of copper or copper coated steel attached to the array of plates, the assembly being fused together to define a combustion chamber with discrete combusted gases and water passages within said assembly.

[0001] This patent application is a continuation application of PCTapplication serial number PCT/AU99/01106 filed on Dec. 14, 1999(published in the English language on Jun. 21, 2001). This patentapplication is a continuation-in-part application of U.S. patentapplication Ser. No. 09/719,675 filed on Feb. 9, 2001, which was a 35U.S.C. §371 of PCT application serial number PCT/AU99/00473 filed onJun. 15, 1999 (published in the English language on Dec. 23, 1999),which claimed the benefit of Australian patent application number PP4105 filed on Jun. 15, 1998. Each of these applications is herebyincorporated by reference.

I. FIELD OF THE INVENTION

[0002] This present invention relates to a fired instantaneous waterheaters and other instantaneous types such as combination boilers,central room heaters, commercial and industrial water heaters and waterprocessing systems to name some others. More particularly the presentinvention relates to a heat exchanger and a water jacket assembly forsuch water heaters. The invention also relates to a method ofmanufacturing such a water heater. These water heaters can be used toheat not just potable water, but mixtures of water and other additiveswhether potable or not. Such instantaneous fired water heaters providehot water on demand.

II. BACKGROUND OF THE INVENTION

[0003] Approximately 70% of the world's manufactured water heaters arebelieved to be of the “instantaneous type” where hot water is providedon demand by use of means to instantaneously heat the water as it flowsthrough the heater. This type of water heater is typically pressuredependent with limitations on the flow rate of hot water it can sustain.One attempt to remedy this has been to increase the cross sectional areaof the passages through the heat exchanger. However this solution hasled to increased susceptibility to scaling and its difficulties in theprior art.

[0004] Also difficulties exist in constructing and assembling costeffective, long life heat exchangers for this type of water heater. Thistype of water heater also generally has combustion chamber surroundswhich have a relatively high heat loss to the surroundings.

[0005] The lack of cost effectiveness relating to construction andassembly result from the fact that prior art instantaneous water heaterheat exchangers are manufactured from a fin and tube construction. Thisis a costly and time consuming construction method.

[0006] Another problem of prior art instantaneous water heaters is thatbecause of a single water path through the fin and tube constructionsuch water heaters experience a significant pressure drop across theinlet and outlet to the heat exchanger. This has the effect on the flowrate of hot water from such heaters as being relatively low compared tomains pressure storage water heaters.

[0007] The construction of prior art instantaneous water heater heatexchangers have been susceptible to scaling. In general terms scaling isknown to occur under conditions of high temperature and high levels ofdissolved solids in the water. Hot spots in heat exchangers,particularly a problem in fin and tube constructions, can result in ahigher incidence of scaling.

[0008] Instantaneous water heaters are common in colder climates as theycan be used for the dual purpose of providing hot water of approximately80° C. for central room heating as well as hot potable water atapproximately 50° C. for cooking and washing.

[0009] Such boilers serving these dual purposes are commonly known ascombination boilers or combi-boilers. One of the particular difficultieswith these systems is that there can be a significant thermal lag on thehot potable water circuit. This thermal lag almost always results inlarge quantities of water being wasted until the hot potable waterarrives at a user's water spout.

[0010] It is an object of the present invention to provide a waterheater, water heater components and manufacturing methods of waterheaters and components, to at least in part ameliorate at least one ofthe difficulties of the prior art.

III. SUMMARY OF THE INVENTION

[0011] The present invention provides a water heater heat exchangerelement to heat water with combustion products being formed from firstand second plates joined together to form at least one channeltherebetween to provide at least one liquid flow path between an inletand an outlet, said flow path being inside of said element and acombustion products heat transfer surface on the outside thereof, saidelement being characterised by said at least one flow path eachconsisting of a single path which extends across a portion of saidelement away from said inlet in one direction and across said portion inthe opposite direction toward said inlet, in a serpentine manner.

[0012] The flow path can extend partially or fully across the width ofthe element.

[0013] The flow path when extending across the plate does so inpreferably a zig zag or sinusoidal configuration. Further the serpentinemanner is such that the flow path winds back over itself at least once,and preferably two to four times. The water flow path is preferablyshaped like one of the following: generally helical; cork screw; squarehelical; or vortex shaped.

[0014] The first plate can have a single continuous groove whereby whena flat second plate is joined thereto, said channel is formed.Alternatively said first and second plates each have a series ofdiscrete dimples therein, whereby adjacent dimples on said first plateare connected by the series of adjacent and partially overlappingdimples on said second plate.

[0015] Preferably the flow path requires liquid flowing therein totravel along one of said dimples in said first plate having a straightline pathway then flow through an approximately 90° direction changeinto said second plate then through an approximately 90° directionchange to flow through an adjacent dimple in said second plate in astraight line pathway through said adjacent dimple.

[0016] The dimples can provide a straight line path after transitionfrom said first plate to said second plate whereby the maximum length ofthe straight line path is in the range of two to ten times the depth orheight of the dimple.

[0017] Preferably the first and second plates each have a flared endextending away from a joining plane of said first and second plates. Theflared ends can extend along the side edges of said plate from saidleading edge to said trailing edge. Also said flared ends can extend fora distance in the direction towards the centre of said plate along saidleading and trailing edges.

[0018] Preferably the element is formed from identical plates placedback to back. The heat exchanger element and or plates forming said heatexchanger element have a nestable shape.

[0019] In one embodiment the heat exchanger element and plates fromwhich it is formed has or have a shape which includes a main portion andat least two arms extending away from the main portion. The at least twoarms can extend in the one of the following directions away from themain portion: parallel to each other; diverging away from each other;converging towards each other; or produces any one of the followingshapes: a Y shape, U shape, C shape, E shape H shape, V shape or anyother appropriate shape. Preferably the arms of the form a water jacketaround a combustion chamber, while the main portion forms a heatexchanger unit. The exchanger element can also have a shape whereby theat least two arms extend in opposite directions to each other, such asin a T shape, with the cross bar of said T shape forming an end wall ofsaid combustion chamber.

[0020] Preferably the element formed includes at least one dimpleformation thereon whereby when two or more of such elements arepositioned side by side, said dimple formations are aligned to form aheader which can receive a liquid and which will direct said liquidthrough each of said heat exchanger elements simultaneously.

[0021] If desired the leading edge of the plates and or the elementformed from the plates or is scalloped or curved so that most pointsalong said leading edge have a minimum distance to the nearest channelsuch that said minimum distances are similar.

[0022] The plates each have a formation to allow all plates to be nestedtogether prior to holding or joining them together. The formation ispreferably a flange on said first and second plates such that whenplaced back to back said flanges all extend in the same generaldirection. The flange is preferably at an angle to said plate. Theflange can extend partially around the periphery of said plates oralternative a wholly around the periphery of said plates, where acombustion products path is provided.

[0023] The heat exchanger elements can be formed from plates made fromtwo or more plate segments which are bonded together to from a compositesingle plate. Such a composite single plate can have different materialsin the different plate segments. The different materials can be chosenon the basis of heat resistance characteristics.

[0024] If desired a series heat exchange elements can have a leadingedge formed of a different material to that portion of the heat exchangeelement which contains said dimples or channels. The leading edges canhave a shape which will help to maintain the temperature in thecombustion chamber in order to promote combustion.

[0025] Heat exchanger elements can include a by pass channel or dimplewhich connects an entry header to an exit header. Further if desired thewater flow paths in the heat exchanger elements can cross over eachother at predetermined points to enable water flowing therein to mixwith, pass through, or pass over and under, each other.

[0026] The invention also provides a water heater heat exchanger elementbeing formed from a first plate and a second plate forming a channeltherebetween to form a liquid flow path inside of said heat exchangerand a heat transfer surface on the outside of said heat exchangerwherein the configuration of said liquid flow path and thus said heattransfer surface is varies across the width of said heat exchangeelement in one or more of the following characteristics: the crosssectional area of the liquid flow path; the angle at which the liquidflow path lies to the leading edge; the length of said liquid flow path;the amount of resistance to liquid flowing in said liquid flow path; theamount of resistance to combustion product passing over the heattransfer surface.

[0027] The first plate can have a single continuous groove wherein whena flat second plate is joined thereto said liquid flow path is formed.Alternatively said first and second plate each have a series of discretedimples whereby adjacent dimples on said first plate are connected bydimples on said second plate to form said liquid flow path.

[0028] Preferably said flow path is of a zig zag or sinusoidalconfiguration. The liquid flow path can be configured to provide at nearto a leading edge thereof longer straight line sections compared withthe length of straight line sections in the vicinity of a trailing edgeof said element. The flow path is preferably a single path which travelsover all or part of said element in a serpentine manner. Preferably saidpath extends across part or all of said element at least two.

[0029] The path can be such that the included angle between lengths ofdimples or segments of channels on said first and/or second plate in thevicinity of a leading edge is varied by comparison to the included anglein the region of a trailing edge. Also if desired the amplitude of saidzig zag or sinusoidal configuration can be varied in said flow path inthe vicinity of said leading edge by comparison to the amplitude of saidzig zag or sinusoidal configuration in the vicinity of said trailingedge.

[0030] If a single path is not utilised the flow path can be dividedinto a multiple number of parallel flow paths connecting a channelacross said elements in the vicinity of said trailing edge to a channelacross said elements in the vicinity of said leading edge.

[0031] Another feature that can be incorporated is that the thickness ofsaid heat exchanger is varied from said leading edge to said trailingedge. Alternatively, the depth of said dimples on said plate or platesis varied from said leading edge to said trailing edge. Preferably whentwo or more elements are positioned adjacent to each other a combustionproducts flow path is formed between adjacent plates, said flow path,near to said leading edges being wider than at said trailing edges.

[0032] Preferably the water heater heat exchanger element as describedabove has a greater than one pair of inlets and outlets so that saidheat exchanger element can have more than one liquid circuit passingtherethrough. Preferably when in use the hottest parts of the heatexchanger element receive a first circuit, while a second circuit isheated in a cooler part of the element.

[0033] The water heater heat exchange element can have, in addition to aseries of discrete dimples, a continuous peripheral path to serve awater jacket function.

[0034] The invention also provides a heat exchanger formed from aplurality of heat exchanger elements as described above, said elementsbeing like oriented in said heat exchanger and placed parallel.Preferably the outside surfaces of dimples of said first plate of oneelement, make contact with outside surfaces of dimples on said secondplate of another element at discrete lines or points of contact. Thediscrete lines or points of contact preferably fused, soldered, brazedor otherwise connected or contacting each other, by such other means asmechanical clamping forces etc.

[0035] The heat exchanger so formed is such that when in use, combustionproducts are forced around said channels and said discrete lines orpoints of contact forming a convoluted combustion path through said heatexchanger.

[0036] The invention further provides a water jacket assembly for aninstantaneous gas fired water heater, the assembly including plateshaving therein an array of dimples, said plates being placed together inpairs, the pairs of plates being arranged in parallel to form a heatexchanger, the heat exchanger being bordered by a water jacket beingformed from plates having therein channels or dimples to allow water toflow through said jacket, said jacket being joined to or integral withthe heat exchanger, said heat exchanger and water jacket having passagesinterconnecting them to allow liquid to pass between the plates, theassembly being held together to define a combustion chamber withcombustion product passages and water passages within said assembly.

[0037] Preferably the water jacket assembly includes a heat exchangeelement or a heat exchanger as described above

[0038] Preferably said water jacket assembly is formed from a pluralityof plates including at least a U or Y shaped plate to form a heatexchanger as described above and at least a T shape plate to form asecond heat exchanger element as described above whereby each of saidplurality of plates are joined back to back with like plates to form aplurality of intermediate and end heat exchange elements, said waterjacket assembly being constructed by sandwiching said intermediate heatexchangers between said end heat exchangers and holding them together.

[0039] The elements can be generally vertically oriented so that whensaid elements are assembled leading edges of said elements are generallyaligned with the depth of said unit; or generally vertically oriented sothat when said elements are assembled the leading edges of said elementsare generally aligned with the width of said unit; or generallyhorizontally oriented.

[0040] If horizontally oriented said elements include aperturestherethrough to permit combustion products to flow between pairs ofelements.

[0041] Preferably the plates of the heat exchanger are adapted to causeturbulent flow of water through the water passages; and or are adaptedto cause turbulent flow of combusted gases past the exterior; and or aresuch that their exterior also provides an escape path for condensatethat in use collects on the external surfaces of the heat exchanger.

[0042] The invention further provides a water heater having a heatexchanger as described above and or a water jacket assembly as describedabove.

[0043] The water heater can include a storage means to receive hot waterwhich would otherwise remain in said apparatus when a user has closed avalve preventing further hot water passing through said valve. The hotwater in said storage means can be passed through said valve once saidvalve is re-opened.

[0044] The present invention also provides a water heater system havingat least two water flow paths, with both paths passing through awater/gas heat exchanger, which transfers heat from combustion productsto water contained in said circuits, a first of said at least two pathsincluding a serial connection to a radiator means and a serialconnection to a water/water heat exchanger where water in said firstpath can transfer heat to or receive heat from water in said secondpath. Preferably said water in said first path is in a closed loop.

[0045] Preferably the second of said at least two paths includes a coldwater inlet. The cold water inlet can split into two water flowsub-paths, a first sub-path to deliver water to said water/water heatexchanger and a second sub-path to deliver water said water/gas heatexchanger. The second sub-path can merge with said first sub path forwater to flow out of said system, when a valve on an outlet conduit fromsaid system is in an open condition.

[0046] When a valve on an outlet conduit from said system is in a closedcondition water in said first and second sub-paths is circulated.

[0047] The invention also provides a water jacket assembly for aninstantaneous gas fired water heater, the assembly including pressedprofiled plates, one plate being the inverted image of the other, saidplates being placed together in pairs, the pairs of plates beingarranged in a parallel to form a heat exchanger, the heat exchangerbeing bordered by a water jacket comprising overlapping side and endpanels of copper or copper coated steel attached to the heat exchanger,the assembly being fused together to define a combustion chamber withdiscrete combusted gases and water passages within said assembly.

[0048] It is preferable that the profiled plates of the heat exchangerare adapted to cause turbulent flow of water through the water passages,and turbulent flow of combusted gases past the exterior, the exterioralso providing escape routes for condensate that in use collects on theexternal surfaces of the heat exchanger.

[0049] It is preferable that the water jacket has a cold water inlet anda hot water outlet, at least one gas burner being positioned within thecombustion chamber whereby cold water flows through the assembly to exitas hot water.

[0050] Preferably, the at least one gas burner is positioned above theheat exchanger and the heater includes a fan that mixes gas with air andforces the gas/air mixture to the burner and, as combusted gases pastthe heat exchanger.

[0051] The invention also provides a method of manufacturing a waterjacket assembly including making profiled heat exchanger plates, placingpairs of plates together to form a heat exchanger element, placing aplurality of heat exchanger plate elements together to form a sandwich,said assembly having a combustion chamber and combustion productspassages and water passages within said assembly and wherein two type ofheat exchanger elements are formed, end elements and intermediateelements with said end elements having a different water path to saidintermediate elements.

[0052] Preferably said heat exchanger plates are manufactured such thatthose portions not required on a blank for one plate are a part of thenext successive plate stamped.

[0053] The heat exchanger elements can be assembled as a set of parallelplates, which can be any one of the following: vertically oriented orhorizontally oriented. If vertically oriented the elements can extendsuch that their leading edges run generally parallel to the width of thecombustion or water heater into which the water jacket assembly will beinstalled. Alternatively vertically oriented the elements can extendsuch that their leading edges run generally parallel to the depth of thecombustion or water heater into which the water jacket assembly will beinstalled.

[0054] According to a further aspect of the present invention there isprovided a method of manufacturing a water jacket assembly comprisingpressing profiled heat exchanger plates, side panels and end panels outof copper or copper coated steel, placing two plates together, one beingthe inverted image of the other to form a pair of abutting plates,placing a plurality of pairs of heat exchanger plates together to form asandwich, attaching the side panels to the sandwich and placing the endplates on each corner so that the side and end panels overlap, holdingthe assembly with a jig, and placing the assembly in an oven for apredetermined time to fuse the copper surfaces together to provide anintegral assembly having a combustion chamber and discrete combustedgases and water passageways within said assembly.

[0055] In accordance with one aspect of the present invention there isprovided an instantaneous gas fired water heater comprising a heatexchanger through which water flows to be heated by a gas fired burner,the heat exchanger having a cold water inlet and a hot water outlet, anair tight chamber positioned downstream of the hot water outlet of theheat exchanger whereby when the demand for hot water ceases, theinternal pressure within the hot water system causes hot water to flowfrom the heat exchanger into the air chamber to reduce the temperatureof the heat exchanger.

[0056] The air chamber preferably comprises a sealed tank that initiallycontains only air, the internal pressure of the system causing the tankto fill when no water is being drawn off and causing the tank to emptyas hot water is drawn off, the tank refilling when demand for hot waterceases.

[0057] According to a further aspect of the present invention there isprovided a water jacket assembly comprising a plurality of heatexchanger plates pressed out of metal, the plates being placed togetherin inverted pairs in parallel, each plate having peripheral sideportions that overlap as the plates are placed together, a pair of endpanels being positioned at the ends of the heat exchanger plates withoverlapping edges whereby the assembly can be placed in an oven on itsend so that the weight of the assembly causes the plates and panels tofuse together to define discrete water and air passageways.

[0058] Preferably the profile of the plates and panels defines a heatexchanger surrounded by a water jacket, the water jacket defining acombustion chamber within the assembly.

IV. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Embodiments, incorporating all aspects of the invention, will nowbe described, by way of example only, with reference to the accompanyingdrawings.

[0060]FIG. 1 is a front elevation view of a water heater being oneembodiment of the invention, with the front portion of its water jacketassembly removed.

[0061]FIG. 2 is a left side elevation of the heater of FIG. 1.

[0062]FIG. 3 is a right side elevation of the heater of FIG. 1.

[0063]FIG. 4 is an exploded perspective view of components of a waterjacket assembly.

[0064]FIG. 5 is a front elevation of a water jacket assembly used in thewater heater of FIG. 1.

[0065]FIG. 6 is a side elevation of the water jacket assembly of FIG. 5.

[0066]FIG. 7 is a plan view of the water jacket assembly of FIG. 5, withthe heat exchanger 51 shown in schematic representation, for a detail ofthe plan view of the heat exchanger refer to FIG. 23.

[0067]FIG. 8 is a diagrammatic cross section through the plate 53 ofFIG. 9 along plane A-A.

[0068]FIG. 9 is a front elevation of the plate 53 of FIG. 4.

[0069]FIG. 10 is a representation of the water flow path as viewed infront elevation formed from plates 53 and 54 of FIGS. 4, 9 and 11.

[0070]FIG. 11 is a rear view of plate 54 of FIG. 4.

[0071]FIG. 12 is a diagrammatic cross section through the plate 54 ofFIG. 11 along plane BB.

[0072]FIG. 13 is a diagrammatic cross section through heat exchangersformed from pairs of plates 53 and 54.

[0073]FIG. 14 is an enlarged view of part of the cross section of FIG.8F.

[0074]FIG. 15 is a diagrammatic perspective view of a heat exchangerassembled from elements formed from pairs of plates 53 and 54 of FIGS.4, 9 and 11 with combustion products and water path ways.

[0075]FIG. 16 is a detail view of three of the dimples of plate 54 ofFIG. 11.

[0076]FIG. 17 is an enlarged view of two whole dimples of the plate 53of FIG. 9.

[0077]FIG. 18 illustrates the dimples of FIGS. 16 and 17 connectedtogether back to back.

[0078]FIG. 19 illustrates portions of plates 53 and 54 (in spaced apartrelation for clarity) indicating diagrammatically the flow path ofliquid through the plates and passages formed when the plates areabutted face to face.

[0079]FIG. 20 illustrates a typical combustion gas flow path over theexternal surface of plate 53 of FIG. 9.

[0080]FIG. 21 illustrates a typical combustion gas flow path over theexternal surfaces of plate 54 of FIG. 11.

[0081]FIG. 22 illustrates the drawings of FIGS. 20 and 21 combinedshowing the convoluted combustion gas flow path between adjacentcontacting elements formed from plates 53 and 54.

[0082]FIG. 23 illustrates a plan view of a heat exchanger made up ofplates 53 and 54 of FIG. 4.

[0083]FIG. 24 is a plan view of a single dimple.

[0084]FIG. 25 is a side elevation of the dimple of FIG. 24.

[0085]FIG. 26 is a cross section through line BB of FIG. 25.

[0086]FIG. 27 is a cross section through line CC of FIG. 25.

[0087]FIG. 28 illustrates a front view of a plate of heat exchangerelement being a further embodiment of the invention.

[0088]FIG. 28A illustrates an embodiment similar to that of FIG. 28except that the straight line path length is varied.

[0089]FIG. 29 illustrates a front view of a plate of a heat exchangerelement of another embodiment having parallel flows therethrough.

[0090]FIG. 29A illustrates an embodiment similar to that of FIG. 29except that the straight line path length is varied.

[0091]FIG. 30 illustrates a side view of a heat exchanger assembly ofanother embodiment.

[0092]FIG. 31 is a left side elevation of an instantaneous gas firedwater heater of another embodiment of the invention.

[0093]FIG. 32 is a front elevation of the heater of FIG. 31.

[0094]FIG. 33 is a right side elevation of the heater of FIG. 31.

[0095]FIG. 34 is a side elevation of a plate that forms part of a waterjacket assembly of a further embodiment of the invention applicable tothe water heater of FIGS. 31 to 33.

[0096]FIG. 35 is a side elevation of an end plate forming part of thewater jacket assembly of FIG. 35.

[0097]FIG. 36 is a side elevation of a pair of end plates of FIG. 35 toillustrate flow path.

[0098]FIG. 37 is an exploded perspective view showing the assembly ofheat exchanger plates and end panels in the water heater of FIGS. 31 to33.

[0099]FIG. 38 is a schematic cross section of stacked plates showingnesting feature.

[0100]FIG. 39 is a side elevation of an alternative form of heatexchanger plate.

[0101]FIG. 40 is a diagrammatic side elevation of the liquid flow paththrough a channel formed by back to back dimples on a pair of plates ofFIG. 39 placed together.

[0102]FIG. 41 is a side elevation of a heat exchanger element plate ofanother embodiment.

[0103]FIG. 41A is a side elevation of an end heat exchanger elementplate for use with the element formed from the plate of FIG. 41.

[0104]FIG. 42 is a schematic circuit illustration showing use of theheat exchanger plate of FIG. 41.

[0105]FIG. 43 is a schematic circuit illustration showing a differentuse of the heat exchanger plate of FIG. 41.

[0106]FIG. 44 illustrates a front elevation of a further embodiment ofthe invention.

[0107]FIG. 45 illustrates a side apparatus view the apparatus of FIG.44.

[0108]FIG. 46 is a sectional view through the apparatus of FIG. 44through the lines M of FIG. 45.

[0109]FIG. 47 is a front elevation of a further embodiment of theinvention showing water flow path.

[0110]FIG. 48 is the front elevation of FIG. 47 showing combustiongasses flow path.

[0111]FIG. 49A is a perspective view of five plates which are used tomanufacture the water jacket assembly 50C of FIGS. 47 and 48.

[0112]FIG. 49B is an exploded view of the water jacket assembly platesformed form the plates of FIG. 49B and as used in the embodiment of FIG.47.

[0113]FIG. 49C is a schematic water flow path through the plates ofFIGS. 49A and 49B.

[0114]FIG. 50 illustrates an accumulator or reservoir for use with thewater heater of previous drawings.

[0115]FIG. 51 illustrates a schematic cross section of a part of a heatexchanger being another embodiment.

[0116]FIG. 52 illustrates a heat exchanger element with a cross overpath.

[0117]FIG. 53 illustrates an end plate with an end plate with a bypassfeature.

[0118]FIG. 54 illustrates a cross section through another embodiment ofa water heater having a water jacket assembly similar to that of FIGS.44 to 46, but with a naturally aspirated burner system.

V. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0119] A domestic water heater 10 is illustrated in FIGS. 1 to 3, and isfuelled by gas and operates to provide an instantaneous flow of hotwater.

[0120] As shown in FIGS. 1 to 3, the water heater 10 is housed in arectangular enclosure 11 that is designed to be mounted flush against anexternal wall. The heater needs to be coupled to a supply of gas and itis understood that the heater can be adapted to work on a variety ofcommercially available gases. The combustion of the air gas mixtureforms combustion products which are vented to the atmosphere via a smallaperture 12 at the front 13 of the heater. Alternatively, the heater canbe installed internally with exhaust gases being vented to theatmosphere via a small flue that would extend either through the wallcavity or up through the ceiling.

[0121] In summary, the water heater 10 has a burner 20 positioned abovea water jacket assembly 50 so that heat and combustion products from thegas burner 20 pass through a heat exchanger 51 that forms part of thewater jacket assembly 50 to heat up a supply of cold water that isarranged to flow through the heat exchanger to exit the heat exchangeras hot water. Whilst having a single burner 20 will be the cheaperconstruction, if desired to allow the water heater 10 to cope with turndown situations, multiple burners (with appropriate controls) can beutilised so as to be able to effectively shut off parts of the burnerthereby allowing optimising of the burners output depending upon needs.

[0122] A control mechanism 32 controls the amount of gas delivered fromconduit 32A and which will ultimately be burned by the burners 20. Theamount of gas burned is dependent on the flow of water and thetemperature requested, ie on demand. The burning capacity of the gasburners is enhanced by the provision of a blower or fan 30 that mixesgas with air before prior to arriving at the burners 20 to ensure use ofthe most efficient air fuel mixture.

[0123] The fan 30 also operates to downwardly force the combustionproducts and hot air generated by the burners 20 in a generally verticaldirection through the heat exchanger 51. The high efficiency of the heatexchanger 51 is such that it can produce condensation which drips downinto a collection tray 71 mounted at the base of the enclosure 11. Thecondensate is directed out of the enclosure 11 by means of a dischargeconduit 72 into a sewerage drain.

[0124] The burner 20 is positioned across the top of the heater 10. Theburner 20 is fed an air gas mixture from a mixing chamber 31, whichreceives gas and air via a modulating gas valve 32 and the electricallydriven fan 30, which mixes the gas with the air prior to feeding theair/gas mixture to the burner 20. The burner 20 is in the form of one ormore ceramic plates 35 having a series of small apertures (not shown)extending therethrough. Whilst a ceramic plate burner construction isdescribed in the embodiment of FIGS. 1 to 3, any burner or multiples orcombinations of burners can be used, such as mesh burners, plateburners, metal screen and mesh burners, carbon fibre burners etc.

[0125] The apertures in the burner provide a very large number of smallflames that project downwardly (as a result of the air/gas mixture flowcaused by fan 30) towards the water jacket assembly 50. In order toensure that carbon monoxide is kept to a minimum the flames terminate inthe combustion chamber 50A at a position that is above the leading edges260 of the heat exchanger 51. The heat exchanger 51 is positioned in thelower half of the water jacket assembly 50. The overall height of thewater heater 10 can be decreased by selecting a burner, such as a meshburner, which will operate with a smaller flame length.

[0126] As shown in FIGS. 1 to 3, the cold water inlet 14 extends intothe base of the water jacket assembly 50 (cut away for illustrationpurposes) on the left hand side thereof as viewed in FIG. 2, with hotwater exiting the water jacket assembly 50 via conduit 15A from theright hand side, thereof towards the top of the heat exchanger 51 at thehot water outlet 15.

[0127] A water flow meter 90 monitors flow of water at the cold waterinlet 14. A first temperature sensor T1 is positioned on the cold waterinlet and a second temperature sensor T2 is positioned on the hot wateroutlet 15 from the heat exchanger 51. A third temperature sensor T3 ispositioned on a water flow control valve 60 which is coupled both to thecold water inlet 14 and the hot water outlet 16.

[0128] The supply of gas flows up conduit 32A from the base of the waterheater 10 along the left thereof side to the modulating gas valve 32 andinto the fan 30 as shown in FIGS. 1 to 3. The hot water outlet 16 fromthe water valve 60 has a first outlet 17 that is designed to providewater up to a temperature of 80° C. and a second lower temperatureoutlet 18 that dispenses water up to a temperature of 50° C. via a flowsensor 19 if the water heater 10 is to provide hot water for radiatoruse as well as potable water. Water heaters of this kind generally havesafety controls to prevent scalding when water of 80° C. can beproduced. When flow is detected in outlet 18 by flow sensor 19, theelectronic control system 80 automatically limits the maximum availabletemperature to 50° C.

[0129] The combustion products generated by burner 20 pass through theheat exchanger 51 and exit the water heater 10 at the base of the heatexchanger 51 via the rectangular outlet 12 in the front face 13. Theseexhausted combustion products exit at a temperature that is close to thetemperature of the cold water entering at inlet 14, thus the loss of theheat to the surroundings is kept to a minimum.

[0130] The electronic control system 80 is mounted near the top of thewater heater 10 as shown in FIG. 1 to control operation of the heater10. To operate, the water heater 10 has to be coupled to a source ofgas, a source of cold water and a source of electricity.

[0131] The water jacket assembly 50, is illustrated in detail withreference to FIGS. 4 to 23 and includes an external water jacket 52 thatsupports an internally located heat exchanger 51 that is in the form ofa discrete number of pairs of rectangular plates 53, 54 (as illustratedin FIGS. 4 and 5) depending on the heat exchanger 51 requirements. Theconstruction of the heat exchanger 51 will be discussed in more detaillater.

[0132] The water jacket assembly 50 in summary has the combustionchamber 50A, the water jacket 52 and heat exchanger 51. These componentsare constructed from 3 differently shaped plates. Two of a first shapedplate form the front plate 100F and rear plate 100R (see FIG. 4 and theassociated description). These first shaped plates are placed back toback to encase opposite sides of the assembly. Four of a second shapedplate form end plates 101A, 101B, 101C and 101D that, as shown in FIGS.4, 5 and 6, envelop and overlap the ends and sides to define the waterjacket 52.

[0133] A plurality of pairs of a third plate defines the heat exchanger51, with only one pair of rectangular plates 53, 54, being illustratedfor convenience and clarity of FIG. 4. The plurality of plates 53 and 54when mounted in spaced apart pairs constitute the heat exchanger 51.

[0134] As shown in FIGS. 5 to 7, the sandwich of the plates which formsthe heat exchanger 51 is located towards the base of the unit. The waterjacket 52 has liquid passageways or channels that run across the bottom,then up to the top of half of the sides 200 then crosses to the otherhalf of sides 200, then across the top of this other half, then down tothe bottom. In the sides 201 and 202 of FIG. 4 the water flow pathbegins at the bottom and flows initially in two directions to the middleof the side 201 and 202, whereupon it follows a single path to the topof the side 201 and 202, then back down to the middle where it will exitthe respective side 201 and 202 to enter the adjacent respective side202 or 201.

[0135] However, in the sides 201 and 202 as illustrated in FIG. 6, whichsides are a little different to those in FIG. 4, the path in the sides200 will terminate near the midpoint of the corners, whereupon the waterenters at a midpoint of the sides 201 and 202 then splits into an upwardand downward path to the go to the top and bottom respectively, thenacross the top and bottom of sides 201 and 202, then back to an exitmidpoint opposite the entry midpoint. The exit midpoint on one side 201or 202 feeds into an entry midpoint on the adjacent side 202 or 201respectively.

[0136] The space bounded by the water jacket 52 and the top of the heatexchanger 51 defines the combustion chamber 50A. The water jacket 52 ispositioned externally of the heat exchanger 51 with the gas flames fromthe burner 20 being produced along the centre line of the water jacketassembly 50 within the combustion chamber 50A. This feature has theeffect of drawing off heat from the gas flames to reduce sideways escapeof heat and also reduce the temperature of the hot gases at the heatexchanger 51.

[0137] As shown in FIG. 5, the cold water enters the assembly 50 fromone side at the base and exits the assembly on the opposite side towardsthe top of the heat exchanger 51. Initially, the water moves in twodirections around the sides and ends of the water jacket 52 so thatwater flows through the whole of the water jacket before passing intothe heat exchanger 51. This reduces the likelihood of the water jacket52 being overheated and reduces waste of hot gases.

[0138] By manufacturing the assembly from three plates that are simplyreversed and or inverted, the whole assembly can be produced from asimple stamping operation. Furthermore, in this embodiment, the assemblyis manufactured from stainless steel plates coated in copper and thecomponents are assembled together by use of a jig (not shown) so thatthe component plates are in abutting contact with all the abuttingsurfaces being copper to copper.

[0139] The assembly is placed in an oven for a predetermined period at atemperature to fuse the copper to provide an integral unit in which allthe components are bonded together and the water and air passageways aredefined accurately with no leakages. There is thus no need for welding,soldering, or other fasteners and this fusing of the copper coatingensures satisfactory operation over a long life. The design of aconvoluted passage for water flow is also specifically designed toencourage turbulent flow to ensure that there are no stagnant waterpockets or hot spots in the heat exchanger 51 or water jacket 52.Furthermore the external shape of the plates provides a convenient routefor run-off of condensate that forms on the exterior of the heatexchanger elements. The water jacket assembly 50 has proved efficientand allows maximum transfer of heat from the gas flames to the waterwithout excessive heat being lost to exhaust.

[0140] While fusing is described with respect to copper other fusingmetals can be used such as nickel or the like. Instead of fusinghowever, any means of holding the plates together which form the waterjacker 52 and heat exchanger 51 can be utilised.

[0141] A gas pressure sensor 84 is positioned at the gas entry of themodulating gas valve 32 to sense a drop in gas pressure to reduce theoutput of the water heater 10 should there be a shortage of gaspressure. Conventional domestic gas pressures are such that if too manyappliances are used at once there is often a drop in the gas pressure.To ensure that a drop in gas pressure does not reduce the temperature ofthe hot water, the gas pressure sensor 84 causes the rate of flow ofwater to be reduced by means of valve 60 to compensate for a reductionin gas pressure so that the water heater 10 operates at the desiredtemperature albeit at a reduced output in terms of liters per minute.Alternatively if a water flow valve 60 is not used, by means of anappropriate signal from sensor 84 the controller 80 can be made todecrease the flow rate of air being mixed with the gas, and or the gasby the valve 32, to form the air/gas mixture, to maintain optimumcombustion.

[0142] Another feature of the gas valve 32 and controller 80 is the useof an oxygen sensor 71A that detects the amount of oxygen in the fluegases. If the oxygen content of the flue gas is either too high or toolow, a signal is fed back to the controller 80 to change the gas flow byvalve 32 to ensure an optimum mixture. The computerised controller 80monitors three temperatures, namely the temperature T1 which is thetemperature at the inlet of the cold water, the temperature T2 being thetemperature which is at the heat exchanger outlet; and the temperatureT3 which is the temperature at the hot water outlet from the waterheater 10. The third temperature monitor T3 is adjustable by a user orservice person to adjust the desired output temperature.

[0143] The controller 80 on sensing the three temperatures can thencontrol the rate of water flow through the water heater 10 and also thegas input through the modulated gas valve 32 and the air input byvarying the speed of the fan 30. The controller 80 varies theseparameters to ensure maximum efficiency.

[0144] A flow sensor 90 is positioned in the cold water inlet 14. Theflow sensor 90 provides an electrical signal which is sent to thecontroller 80 to control the operation of the water heater 10 inrelation to demand. It will also be understood that with this flowsensor 90 can produce a signal to give a visual indication, or beprocessed to give a visual indication, of the rate of flow which can bedisplayed at the water heater 10 and/or at remote locations.

[0145] The flow control valve 60 as illustrated in FIG. 1 is provided tocompensate for too much demand for hot water, or to reduce flow, or ifthere is a danger of the water exceeding the maximum design temperature.In these cases the valve 60 can be made to open or close as theconditions require.

[0146] To start up the heater, an electrically operated ignition systemis (such as a spark igniter or glowing surface or HSI [hot surfaceignition] or any suitable system) is utilised in the combustion chamber50A and the control system 80 ensures that when a hot water tap isopened causing flow of water, there is first a pause to purge anycombustible gases within the combustion chamber. Then depending on theignition system used there may be a short pause during which theelectrically operated ignition system activates and commences to ignitethe air/gas mixture otherwise the air/gas mixture enters the combustionchamber and is ignited. In this embodiment a spark igniter is preferredas it has no lag time to operate.

[0147] If combustion does not start the water heater 10 shuts down thegas flow and the whole process is repeated. The control system can beprogrammed so that if this fails a predetermined number of times thenthe water heater 10 shuts down and a warning light comes on warning theuser of the system that a service call is required.

[0148] To construct the water jacket 52 as illustrated in FIGS. 4 to 7,the water jacket 52 is made from a plurality of two types of plates. Thefirst type of plate is that which makes plate 100F and 100R which hasthree sides, a middle side 200 forming the front and rear faces of thewater jacket assembly 50 and the outer sides 201 and 202 at right anglesto the side 200. When assembled, the side 201 on the front plate 100F islocated adjacent to side 202 on rear plate 100R on the left side andvice a versa on the right side of the water jacket assembly 50 asillustrated in FIGS. 4 and 7.

[0149] A series of channel formations, generally designated by numeral204, are formed in the front plate 100F and are constructed so as tohave depth into the page as illustrated in FIG. 4. While in the rearplate 100R (which is identical to plate 100F) the channels 204 areformed so as to have depth out of the page of the drawings. The channels204 are at the front and rear of the combustion chamber 50A and definethe combustion chamber 50A therebetween.

[0150] To complete the water jacket 52 four identical second platesillustrated in FIG. 4 as plates 101A, 101B, 101C and 101D are orientedand positioned on the front and rear plates 100F and 100R so that theirrespective corners 205 and 206 are positioned onto front and rear plates100F and 100R at corresponding respective corners 205R, 205L, 206L and206R. The plates 101B and 101C as illustrated in FIG. 4 have theirchannels, which are generally designated by the arrows 208, formed suchthat the depth of the channels away from the plate is out of the page inFIG. 4. Whereas the plates 101A and 101D have their channels generallydesignated by the arrows 208, such that the depth of these channels 208are formed into the page.

[0151] The channels 204 and 208 will form a sealed flow path wherebythose portions of the channels 208 on all plates 101A, 101B, 101C and101D in the top half U of the jacket 52 will form double depth channelswith the channels 204 on the front and rear plates 100F and 100R. Thedouble depth channels are in the vicinity of or adjacent to thecombustion chamber 50A and are required to obtain increased flow ratesof water through these portions of the channels to enable thewithdrawing of a significant amount of heat being generated immediatelyaround the combustion chamber 50A.

[0152] In the lower half L of the plates 101A, 101B, 101C and 101D ahalf width channel is formed between the channels 208 and the flat platearea 210 on the middle sides 200 of front and rear plates 101 F and 101R. Half depth channels are also formed on the left and right sides ofthe water jacket 52 by both the upper half U and lower half L of plates101A, 101B, 101C and 101D.

[0153] As illustrated in FIG. 4 , and FIGS. 8 to 23, each pair ofgenerally rectangular plates 53 and 54 are positioned in abuttingcontact to define a convoluted water path therebetween. The two plates53 and 54 are identical. One plate has been inverted and placed back toback with the other so that the corners UL, LL, UR and LR on the plate53 are placed adjacent to the respective corners LL, UL, LR and UR onthe plate 54 (which is simply an inverted plate identical to plate 53).

[0154] The expression ‘back to back’ in this specification and claimssignifies the procedure of aligning plates, or the arrangement ofaligned plates, whether identical or not, so that the concave sides ofthe dimples or channels formed in or on the plates are brought togetherto define a channel or flow path between the dimples or channels.Examples of back to back formations can be seen in FIGS. 4, 23, 30, 37and 38.

[0155] The plate 53 (and likewise 54) has an array of discrete dimples220, which have their longitudinal axis at approximately 45 degrees tothe direction of flow of combustion products. The dimples 220 are all ofsimilar size, width, depth and length and are angled at approximately45° to the longitudinal axis of the plates 53 and 54. There are also oddshaped dimples, some of which have other purposes as described below,while others just serve as interconnections between different paths onthe plates.

[0156] The dimples 220 in plate 53 have their depth out of the page ofthe illustration, whereas because the plate 54 has been inverted, thedimples 220 of plate 54 have their depth into the page of FIG. 4.

[0157] When the plates 53 and 54 are joined together as illustrated inFIGS. 5, 13, 15 and 23 a channel or flow path is formed by the dimples220 on plate 53 and dimples 220 on plate 54. Any two adjacent dimples220 on plate 53 are interconnected by a corresponding dimple 220 onplate 54 so that water can flow from a first dimple in plate 53 alongthat dimple into the connecting dimple on plate 54, then along thatdimple and out of plate 54 and back into plate 53 but into the nextadjacent dimple to the first dimple mentioned on plate 53.

[0158] In this way, as illustrated in FIG. 10 there is formed a flowpath which has a zig zag or sinusoidal configuration when viewed fromthe front of the heat exchanger 51. This is better illustrated withrespect to FIG. 16 to FIG. 19.

[0159] Water, after passing through the jacket 52, enters the heatexchanger 51 made up of a series of heat exchanger elements asillustrated in FIG. 14, such that the dimple formation 230 and 231 matesrespectively with dimple formation 231 and 230 on the plate 54. When theplates are placed adjacent to each other and fused or otherwise heldtogether in a leak proof manner, as in FIG. 13, FIG. 15 and FIG. 23, anupper header 232 is formed (from dimple 231 on plate 53 and dimple 230on plate 54) and a lower header 233 is formed across the heat exchange(made up of dimple 230 on plate 53 and dimple 231 on plate 54).

[0160] Water leaves the water jacket 52 via port 240 in FIG. 4 andenters the lower header 233. From the lower header 233, water will flowthrough each of the heat exchangers (made up of pairs of rectangularplates 53 and 54) and as illustrated in FIG. 10 will follow a zig zag orsinusoidal path when viewed in front elevation. The water will flowacross the width of each heat exchanger element firstly along, flow path242 near to the trailing edge of the heat exchangers; then into path 243where it travels back across the width to the right hand side of theheat exchanger elements; then back along flow path 244 across the widthto the end of the heat exchanger element opposite to the headers 233 and232; and finally along flow path 245 back to the upper header 232.

[0161] As illustrated in FIG. 14, the dimples 220 form a channel throughthe both the plates 53 and 54 with the last portion of the flow pathbeing illustrated. The water flows from the interior 220A″ and crossesover to the interior 220A′ and then into the interior of the differentlyshaped dimples 231 and 230 which form upper header 232 (see FIG. 10).Whereas the combustion products travel through the passages 220B intothe page of the illustration. This flow path (which is further describedbelow) is repeated to make up each of the paths 242, 243, 244 and 245.

[0162] As illustrated in FIG. 15 hot combustion gases X flow downward inFIG. 15 and pass over the leading edges 260 of each of the heatexchangers formed from pairs of plates 53 and 54. The combustionproducts flow through the heat exchanger 51 with a flow path asdescribed in more detail with respect to FIGS. 20 to 23, until they passover the trailing edges 261 of each of the elements formed from theplates 53 and 54. Simultaneously the water enters the heat exchanger 51through entry 56 being on the outermost side of lower header 233. Thewater then flows through the paths 242, 243, 244 and 245 in each of theheat exchangers making its way via a zig zag/helical orsinusoidal/helical serpentine path up to the upper header 232 where itwill exit the heat exchanger 51 by the outlet 57, which is on the sameplate and heat exchanger that inlet 56 is formed on. If desired theinlet and outlet 56 and 57 can be located on opposite sides, and if thenumber of paths were to be varied, could even be located on oppositeends of the heat exchanger 51.

[0163] The following will describe in more detail the water flow paththrough paths 242, 243, 244 and 245. As illustrated in FIG. 16, FIG. 17and FIG. 18, the water will flow in the direction of arrows 250 in thedimples 220 in plate 53, whilst in plate 54 the water will flow in thedirection of arrows 251 as illustrated in FIG. 16. The combination ofthese two flow paths are shown in FIG. 18 (as if the plates 53 and 54were transparent) and in the exploded three dimensional view of FIG. 19.It can be seen that the flow path is such that after travelling throughone of the dimples 220 in the plate 53, the water must change directionby approximately 90° to its direction of flow in the dimple 220 in plate53 to enter the dimple 220 in plate 54. Once in plate 54, the flow willhave to change direction again by approximately 90° for the flow totravel along the dimple 220 in the plate 54 and so on creating a complexconvoluted flow path which can be described as generally helical, orcorkscrew, or possibly even of a square or rectangular helical shape orother three dimensional flow path.

[0164] The dimples 220 have a length as illustrated in FIGS. 24 to 27 ofapproximately 24 mm, however, the straight line path length of thedimple 220 when a water path is formed is of only approximately 15 mmbecause after a maximum of 15 mm travel, water will have to changedirection when flowing in the dimple 220. The depth of the dimple 220out of the plate on each plate is approximately 3.5 to 4.5 mm. It hasbeen found that by sizing the straight line length of travel in thedimples 220 to being in the ratio of approximately 2 to 10 times thedepth of the dimple 220 there results a high level of mixing of thewater flowing through the flow path thus ensuring even distribution ofheat and prevention of hot spots to minimise the risks of scalingoccurring in the heat exchanger 51.

[0165] Once water has passed through the heat exchanger elements, theupper header 232 is connected to the outlet 15 of previous Figures todeliver water to the user or for the temperature to be sensed and outputflow monitored. When adjacent heat exchanger elements are assembled asillustrated in FIG. 13, FIG. 15 and FIG. 23, a convoluted combustion gasflow path is formed over and around the external surfaces of the dimples220 as illustrated in FIGS. 20 to 22.

[0166] As seen in FIGS. 20 to 22, the fan 30 will cause combustionproducts to pass over the leading edge of the heat exchanger elementsand if the adjacent elements are arranged such that the externalextremity of the outside surface of dimple 220 contacts the extremity ofthe external surface of an adjacent dimple 220 (on an adjacent heatexchanger element) then combustion products will flow around respectivedimples 220 as illustrated in FIG. 20. If a gap were provided betweenadjacent heat exchangers, then combustion products would flow not onlyaround individual elements 220 but also between dimples 220 on adjacentplates effectively flowing over as well as around the dimples 220.

[0167] Illustrated in FIG. 21 is a similar flow path over the plate 54which helps to provide an even more complex flow path between adjacentheat exchanger elements when plate 53 on one element contacts plate 54on an adjacent element to produce a flow path as illustrated in FIG. 22,which is highly a convoluted flow path and as illustrated is the paththat can be present between adjacent elements formed from plates 53 and54.

[0168] The combination of the convolute and tortuous combustionproducts' flow path, together with the serpentine and zig zag/helicalwater flow path, results in the heat exchanger 51 being extremelyefficient to the point where, by the time the combustion products havepassed from the leading edges 260 to the trailing edges 261, thecombustion products will have been cooled to a temperature whereby theymay condense on the heat exchanger 51 in the vicinity of the trailingedge 261.

[0169] Further, by drawing off the hot water for domestic use from theupper header 232 after the water has passed along the element near tothe leading edge 260, the water will be at the highest temperaturepossible.

[0170] The plates 53 and 54, as illustrated in FIG. 4 have a flared endor flange F (which is also visible in FIG. 14) that serves two purposes.The flange F forms a double width flange on the heat exchanger elementwhen the two plates 53 and 54 are placed back to back as illustrated inFIG. 14. This double width flange helps to provide greater surface areathrough which heat can be exchanged between the heat exchanger 51 andthe water jacket 52. As the flange F extends a part of the way acrossthe leading and trailing edges 260 and 261 as illustrated in FIG. 4, theportion of the flange F which does this effectively acts like a dam orflow director which is useful to direct the flow of combustion productsover the external surfaces of the dimples 220.

[0171] Illustrated in FIG. 28 is a heat exchanger element 300 which isconfigured differently to the heat exchanger element made from plates 53and 54 of the previous Figures. In this heat exchanger element 300, alower header 233 is provided and an upper header 232 is also provided ina similar manner to that of FIGS. 4, 9, 10 and 11. Also, the flow pathsegments 342, 343, 344 and 345 double back across the heat exchanger 300in a serpentine fashion as in the previous embodiment. The differencebetween the heat exchanger element 300 of FIG. 28 is that a zigzag/helical water flow path segments 342, 343, 344 and 345 provided, issuch that the included angle 301 between the straight line sections ordimples 220 in path 342 is a larger angle compared to the included angle302 in the path 243 above or the included angle 303 in the path 344, orthe angle 304 in the path 345 closest to the leading edge 260.

[0172] By varying the included angles 301, 302 and 303 in respectivepasses across the heat exchanger 300, even greater efficiency can beprovided ensuring that the water passing, for example, through the path345 near to the leading edge has a longer path to travel and possiblypassing through the leading edge segment at a slower rate than throughthe flow path segment 342 at the trailing edge segment. This can helpheat transfer process such that it may cause the combustion products tocondense. The plates used to make the heat exchange element asillustrated in FIG. 28 are identical.

[0173] Illustrated in FIG. 28A is a heat exchanger element 300 which issimilarly configured to the embodiment as illustrated in FIG. 28 andlike part have been like numbered. The difference between the heatexchanger element 300A of FIGS. 28A and 300 of FIG. 28 is that at thetrailing edge there is provided a flow path which begins from the lowerheader 233 and has full depth (that is on each of the plates dimples ora channel of equal depth are formed so that when they are placedtogether, a flow path results of a depth equal to twice the depth of onedimple or channel ). The first flow path 342A is generally of a straightconfiguration and runs across the full width of the heat exchanger 300A.While a full depth flow path is described, it may be necessary to eithervary the depth or size it appropriately to ensure that a combustionproducts' flow path will be formed which will not be constricted to thepoint of preventing the escape of combustion products.

[0174] Upon reaching the side opposite to the header 233, a zigzag/helical water flow path is provided, wherein the included angle 301between the straight line sections is a relatively large angle comparedto the included angle 302 in the row above or the included angle 303 inthe row closest to the leading edge 260. The flow path segments 342A,343A, 344A and 345A double back across the heat exchanger 300A in aserpentine fashion as in the previous embodiment.

[0175] By varying the included angles 301, 302 and 303 in respectivepasses across the heat exchanger 300A, better efficiency can result,ensuring that the water passing, for example, through the leading edgehas a longer path to travel and thereby remains in the combustionproducts' flow path longer than through the flow path segment 342 at thetrailing edge segment. This can help the heat transfer process byproducing greater mixing and turbulence such that it may cause thecombustion products to condense. Further The angles need not be suchthat angles 301>302>303, as circumstances may arise where a differentrelationship is found to be advantageous given the design criteria andconditions to be worked with.

[0176] The effective cross-sectional area of the flow paths 342A, 343A,344A and 345A can also be varied according to the requirements ofoperation of the heat exchanger. Also if desired, the amplitudes A, Band C of paths 343A, 344A and 345A might also be varied to optimise theefficiency and heat transfer.

[0177] Illustrated in FIG. 29 is a heat exchanger element of a furtherconfiguration useable with the present invention. The heater exchangerelement 400 has an upper header 232 and a lower header 233, however, inthis embodiment a lower header channel 442 is provided running fromlower header 233 substantially parallel to the trailing edge 261 whilstan upper header channel 445 runs back to upper header 232 in a directionsubstantially parallel to the leading edge 260 of the heat exchanger.

[0178] Between the lower header channel 442 and upper header channel 445are a plurality of flow paths 443. In this embodiment, water enters theheat exchanger element 400 from the water jacket 52 via lower header 233and fills the lower header channel 442. As combustion products areflowing from the top of the page through to the bottom, the mostefficient direction of movement of liquid in the heat exchanger element400 is in the opposite direction and thus by the arrangement illustratedin FIG. 29, water travels through the flow paths 443 from lower headerchannel 442 up to upper header channel 445 and out of the heat exchangerelement 400 via upper header 232.

[0179] It will be noted in the FIG. 29 that the flow path has a constantzig zag or sinusoidal path wherein the amplitude D of the zigzag/helical flow path measured is constant as is the included angle 401between connecting dimples on the two plates

[0180] Illustrated in FIG. 29A is a heat exchanger element of a furtherconfiguration which is similar to that of FIG. 29, with like parts beinglike numbered. The differences between the elements of FIGS. 29 and 29Ais that in FIG. 29A the flow path has a decreasing zig zag or sinusoidalpath wherein the amplitude of the zig zag/helical flow path measured inthe region D closest to the trailing edge, E in the middle and F at theleading edge are decreasing in size across the height of the heatexchanger element 400A. Also the included angle 401 and other includedangles 402 and 403 are varied to minimise back pressure and/orresistance to flow through the heat exchanger 400. While the amplitudesD, E and F and angles 401, 402 and 403 are illustrated as decreasing insize it is sufficient that they can be varied to produce results to suitthe requirements demanded or desired from the heat exchanger 51.

[0181] As illustrated in FIG. 30, is another variation which can beapplied to the heat exchanger elements and thus the heat exchanger 51 ofFIGS. 4, 8 to 23, 28 and 29. In FIG. 30 it can be seen that in the flowpath 245, 345 or 445 of the previous embodiments, that the depth G ofthe flow path in the trailing edge 261 portions is greater than thedepths H, I and J which progressively get smaller upwardly to theleading edge 260. When heat exchanger elements are placed adjacentlytogether, what results, as illustrated in side view in FIG. 30 is acombustion gas pathway 350 which decreases in volume from the leadingedge 260 to the trailing edge 261.

[0182] As illustrated in FIG. 30, it can be seen that the crosssectional area of the flow path depth closest to the leading edge isgenerally smaller than the rest of the flow paths. The flow path depthcan be sized so as to ensure that water passing therethrough will besufficiently turbulent to increase the probability that thermal boundarylayer mixing will occur. While the depths G, H I and J are decreasing insize in a particular direction, it may be advantageous to have thevariation occur in some other pattern depending upon the requirementsdemanded or desired form the heat exchanger 51

[0183] By producing higher turbulence within water flow paths, theprobability of scaling will be reduced. By also providing a tortuous orconvoluted path such as a zig zag/helical path as previously describedin the area closest to the leading edge, a high level of turbulence canbe created. Whereas in the channels closest to the trailing edge, (withdepths I, H and G) the risk of scaling is less likely in view of thelower temperatures found at these locations and thus if these dimplesand the formed channels are longer or of larger cross sectional area,this may be of little consequence as the risk of scaling is diminished.By having longer or larger cross sectional area of channels on the coolside of the heat exchanger elements this is an opportunity to reduce thepressure drop, whereas in the prior art the fin and tube constructiongenerally has the same size tube all the way through.

[0184] Illustrated in FIGS. 31 to 33 is an instantaneous gas waterheater similar to that of FIGS. 1 to 3, except that the combustionchamber 50A, water jacket 52 and heat exchanger 51 are formed in adifferent manner. Like parts between FIGS. 31 to 33 and 1 to 3 have beenlike numbered and their function and purpose need not be describedfurther as reference can be made to earlier description.

[0185] The water heater 10A of FIGS. 31 to 33 differs from the waterheater 10 of FIGS. 1 to 3 in that a cold water bypass conduit 81 in theform of a tube directly communicates with the cold water inlet 14 andfirst and second water outlets 17, 18. There is a pressure drop acrossthe heat exchanger where the pressure at the inlet 14 is greater thanthe pressure at outlets 17 and 18. This is a result of loss in pressurecaused by the zig zag/helical flow path is tortuous or convoluted naturethrough the heat exchanger 51. Cold water bypasses the heat exchanger 51through the bypass conduit 81 and mixes directly with hot water prior toexit 18 from the water heater 10A thereby increasing the outflowpressure. Mixing cold water with the hot water at the outlet 18 will ofcourse mean that the outlet water temperature is decreased. This can besimply compensated by increasing the heating temperature at the gasburners 20 so that the overall effect is hot water leaving the waterheater at a desired temperature but having a greater pressure.

[0186] Flow valve 82 on the cold water bypass conduit 81 determines theamount of cold water supplied to the hot water outlets. It is understoodthat the greater cold water pressure, the greater will be the hot waterdelivery pressure at the outlet 18. The valve 82 can be manuallyadjusted by a technician at the time of installation of the water heateror during maintenance visits. Alternatively, the valve 82 can beautomatically adjusted in response to fluctuating inlet water pressuremeasured by a sensor (not shown) at the inlet.

[0187] In the embodiment illustrated in FIGS. 31 to 33 the water jacketassembly 50′ is constructed from a plurality of two different plates 550of FIGS. 34 and 560 from FIG. 35. The plate 550 of FIG. 34 that makes upthe central portion of the water jacket assembly 50′ is of a generally Yshaped appearance. Each plate 550 includes a central body portion 551with a pair of upwardly extending arms 552 and 553 that define a bightor space 54 therebetween.

[0188] When a plurality of plates 550 are placed back to back in pairs,a series of heat exchanger elements 570 are formed (as illustrated inFIG. 37 where only 3 pairs are illustrated for convenience) which formthe central portion of a water jacket assembly 50′.

[0189] Illustrated in FIG. 35 is the plate 560 which is of a generally Tshaped appearance. The plate 560 differs from the plate 550 in that atthe base of the T in plate 560 there are no dimples and thus no channelsformed in the middle portion, unlike in the base of the Y of the plate550. This is because this flat region on the plate 560 is adjacent thebase of the Y of plate which will extract heat from the combustionproducts thus making the base of the T of plate 560 redundant in theheat scavenging process.

[0190] Thus to complete the water jacket assembly 50′ of FIG. 37, fourplates 560 are arranged placed in pairs and oriented back to back toform the end heat exchanger elements 580 of FIG. 38. These elements 580have a different structure and configuration to the elements 570 due tothe differences in structure and configuration of the plates 550 and560, as is described below.

[0191] It will be noted that the plates 550 and 560 have an unbrokenchannel 244 and 244A which runs around the outer periphery of the plates550 and 560. This unbroken channel 244 and 244A forms a water jackettype flow path.

[0192] In plate 550, water fills lower header 233 and travels throughthe first row of dimples and the channel formed therefrom, upwardstoward the upper header 232, then to the right of the plate in a “leftand right” circuitous path 243 back down the left hand half of the plate550 until it connects with the base of continuous path 244 on the outerperiphery of plate 550. Once in the path 244 the water travels to thetop of the arm 552 then back down arm 552 through path 245 and adjacentthe leading edge 260 to upper header 232. A mirror image of this path isfollowed on the other half of the plate 550.

[0193] By contrast the plate 560 of FIG. 35, when two plates 560 areplaced back to back (as illustrated in FIG. 36), a lower header 233 isformed with water exiting to the left side of the lower header 233following a continuous path 244A around the left hand side outerperiphery of the plate 560 to the top of plate 560. At this point theflow path 245A takes the water in a downward direction until flow path243A which takes the water in an upward direction and so on throughdownward path 242A, upward path 241A then back down through downwardpath 240A to upper header 232.

[0194] These serpentine flow path formations in the plates 560 and 550result in an effectiveness which is added to by the convoluted flow pathof similar shape to the previously described paths of previouslydescribed embodiments.

[0195] As shown in FIG. 38 two plates 550 are reversed which will allowthem to be pressed and fused together to form joined pairs with flowpaths therethrough. The plates 550 are made such that the dimpleportions are identical, but during the manufacturing process flanges 600(which will be described in more detail later) are oriented in differentdirections (thereby making the plates no longer identical) so as to forma front and back or a left and right side plate, which will be placedback to back to form a heat exchanger element. The pairs of Y shapedplates 550 are arranged in a vertical orientation and in parallel toform a combustion chamber 50A between the arms of the Y shape which formthe front wall 100F and the rear wall 100R of the water jacket 52. Thewater jacket assembly 50′ is completed by placing two pairs of plates560, one pair on each end of the assembly to close off the waterpassageways and to create end walls 100LS and 100 RS of the water jacket52 thus forming the combustion chamber by completing the water jacket 52therearound.

[0196] The water jacket assembly 50′ is thus defined as a blockcontaining a rectangular combustion chamber 50A bounded by a waterjacket 52 defined by the walls 100LS, 100RS, 100F and 100R formed fromthe arms 552 and 553 of Y shaped plates 550 and the ends by pairs of endplates 560. The base portion 551 of the Y shape contains a rectangularblock that constitutes the heat exchanger 51.

[0197] One of the advantages of the Y and T shaped plates 550 and 560 isthat the stamping, forming and separating process can be performed witha minimum of waste of material. The Y shape in particular has theadvantage that the arms of the Y are formed from those positions cutaway from the base of the Y of the previous plates in the stamping orguillotining process.

[0198] After the plates 550 and 560 have the dimples (as illustrated inFIGS. 34 and 35) formed in individual plates 560 and 550 by a stampingprocess, the flanges 600 can be bent so as to form an angled flangewhich is best illustrated in the schematic cross section of FIG. 38.

[0199] As can be seen from FIG. 38 each plate 550 and 560 has a flange600 which nest together. The angled flanges 600 are all oriented in thesame direction irrespective of which plate is considered. This flange600, provides the nesting ability of the plates 550 and 560, and thushelps to form the water jacket assembly 50′ of FIG. 37, with arelatively strong periphery due to the overlapping of these flanges 600.

[0200] The angled flanges are arranged to overlap each other as theplates 550 and 560 are placed together in a sandwich. The angled flanges600 have a slight taper of approximately 5 or 10 degrees so that theplates 550 and 560 can be loosely placed together in a wedgedarrangement. By locating a bead of copper or nickel or other suitablematerial between adjacent flanges or using a copper or nickel coatedstainless steel and heating and applying pressure simultaneously, fusionof the plates 550 and 560 will result in a water jacket assembly 50′ asillustrated in FIGS. 31 to 33.

[0201] The gas burners of the heater are located in the combustionchamber 50A and the interior surface can be lined with a box-likestructure 610 (FIG. 37) having metal gauze 612 to isolate thecomparatively cold surfaces of the heat exchanger 51 from the very hotsurface of the gas burner. The gauze has the effect of ensuring goodcombustion at the gas burner which could be detrimentally affected bythe cold surface of the heat exchanger 51.

[0202] In the embodiment described above the plates 550 and 560 arepreferably pressed out of stainless steel or copper coated stainlesssteel. In another option, each panel 550 and 560 can be made ofcomposite materials so that the hotter part of the panel, namely theupper portion including the arms 520 and 530 can be made of a material,such as those stainless steels or titanium and its alloys specificallydesigned to resist high radiant and convectional temperatures whilst thelower main body portion 51 of the panel would be manufactured of amaterial that does not need to withstand particularly high temperaturessuch as 316 stainless steel. This feature allows efficient use ofmaterials and reduces overall costs. The panel could be stamped/pressedin two halves which are then brazed or fused together. This is bestillustrated with respect to FIGS. 47, 49A and 49B and its associateddescription below.

[0203] While the embodiment above describes generally Y shape and Tshape plates and heat exchanger elements, it will be understood that anyshape which has a main portion and at least two arms extending therefrom can be utilised. The two arms can extend in the one of thefollowing directions away from the main portion: parallel to eachother,; in opposite directions to each other; diverging away from eachother; converging towards each other; or can extend so as to produce anyone of the following shapes: as a T shape, Y shape, U shape, C shape, Eshape, H shape, V shape or any other appropriate shape.

[0204] In the embodiment shown in FIGS. 39 and 40 a water jacketassembly 170 is constructed in a similar manner to the assemblydescribed with reference to the embodiments above. However, in this casethe plates 150 are of a U shape with a rectangular base structure 151with a pair of upstanding arms 152, 153. As in the previous embodimentand the embodiments described below, the plate 150 illustrated and theheat exchange element made therefrom form intermediate elements. The endplates will be similarly structured to the plates 150 except that thebase 151 will have no dimples, as dimples and channels are somewhatredundant on the end plates in those regions other than the water jacketregion, due to the effectiveness of the water jacket assembly formedtherefrom.

[0205] The base structure effectively defines the body of the heatexchanger whilst the arms 152, 153 define the water jacket and theperiphery of the combustion chamber in the same manner as the embodimentof FIGS. 31 to 38. The plates are superimposed in the same manner as theprevious embodiment and similar manufacturing techniques can be used toensure that the assembly is produced, or if desired without the need forbrazing or welding, by mechanically clamping the plates and thus theheat exchange elements together. A cold water inlet 233 is positionedcentrally at the base of the unit whilst the hot water outlet 232 ispositioned also along the centre line of the top part of the rectangularheat exchanger element base structure 151. The combustion chamber is ofrectangular configuration and houses the burner in the same manner asthe embodiments described above.

[0206] One of the main problems with instantaneous hot water systems isthe breakdown of the heat exchangers caused through either componentsoverheating or more particularly by the build up of scale. Many watersupplies contain high concentrations of dissolved solids and once wateris heated to a temperature which changes the water's chemistry theprobability will be increased that scale deposits will form on theinterior surfaces of the passageways of the heat exchanger until thosepassageways become clogged and fail.

[0207] One means of reducing the likelihood of build up of scaledeposits on the interior surfaces of the heat exchanger is to ensurethat the water is heated evenly by preventing hot spots on the heatexchanger. One way to do this is to provide turbulent flow of waterthrough the heat exchanger. The turbulence of the flow reduces thelikelihood of scale deposits and tends to sweep particulate material outthrough the system. Consequently, the profile of the water passagewaysin the heat exchangers is sufficient to optimise the possibility ofturbulence and to increase thermal boundary layer mixing which alsoenhances heat transfer and reduces the probability of scaling.

[0208] Another means thought to be able to reduce the likelihood ofscaling is to split the water flow path in the heat exchanger into twoseparate water passageways. Such a splitting of the water path circuitcan be useful in combination or combi-boilers or heaters which providewater at approximately 80° C. for radiator usage which may be used incentral room heating and at 50° C. for potable water uses.

[0209] Such a splitting of the water flow path is illustrated in FIG. 42where a heat exchanger 51 made from plates 550A and 550B (see discussionwith respect to FIGS. 41 and 41A below) has two water flow pathstherethrough. The first water flow path is labelled with numeral 701 andthe second with label 703. The water flow path 701 is a closed loopwhile water flow path 703 contains an open loop.

[0210] In water flow path 703, cold water 709 enters the flow path 703and is divided into two conduits 711 and 713 at junction 710. When a hotwater tap connected to hot water outlet 719 is open cold water 709 willflow into both conduits 711 and 713. Conduit 711 passes water into theheat exchanger 51 to those areas near to the trailing edge 261. When thehot water tap is open, water will flow through conduit 713 into potablewater passages 717 of a water to water heat exchanger 716. The heatexchanger 716 also has heating water passages 717A through it for thewater in circuit 701 to heat the water in passages 717, and visa versaas will be described below.

[0211] The water which may be heated in coil 717 passes via conduit 714to meet up with water coming from the heat exchanger 51. The mixing ofthe two flows takes place at junction 718 so that the combined hot watercan flow out of the water heater via outlet 719.

[0212] Cold water bypasses, such as those described previously withrespect to other embodiments, can be included together with temperaturesensing, etc to ensure that the exiting water is cooled, if necessary,to the desired output temperature and to provide the best possible flowrate of hot water. The water, which flows through conduit 711 into theheat exchanger 51, passes through those parts of the heat exchanger 51heated by combustion products that are initially cooled by the waterflow path 701 in the hottest parts of the heat exchanger 51.

[0213] The closed loop water flow path 701 contains water preferablywith glycol (or similar additive) for the purpose of reducing thelikelihood of scaling. The water flow path 701 includes a seriesconnection to a radiator 705, a pump 707 and heat exchanger 716. Inoperation, the water flow path 701 will deliver water along conduit 701Bto the outer side of the heat exchanger 51. The heat exchanger 51 waterflow path passes from the entry point up to the top of the water jacketassembly, then down the side of the combustion chamber through the waterjacket, then through the hottest part of the heat exchanger 51 near tothe leading edge 260, then up the other side of the water jacket andthen delivers water at a desired temperature to the radiator 705, whichcan be used for central room heating radiator. All the time thecombustion chamber is functioning, the pump 707 is circulating waterthrough the water flow path 701.

[0214] After the water has passed through the radiator 705 (and theradiator is functioning) the water temperature will have dropped. Thetemperature of the water that exits the radiator 705 will more thanlikely be above the water temperature of the water in the conduit 713passing through heat exchanger 716. If the water temperature in passages717A is higher than water in passages 717 then water in passages 717will be heated by water in passages 717A.

[0215] If valve 719 were to be closed however, without pump assistance,water would not circulate in water flow path 703. Thus, a pump 712 isprovided to circulate water through the flow path 703, conduits 711, 713and 714 and passages 717. The pump 712 can be made to automaticallyswitch on once no flow is detected in hot water outlet 719. In this way,if the temperature in 717A were less than 717, the water in the waterflow path 703 (which is temporarily in a closed condition) will continuecirculating and dissipating heat to the water from heat exchanger 717into 717A. This process will keep water in a relatively hot condition,that is approximately 50° C. in the closed loop. This also has theeffect that the heat exchanger elements made up of plates 550A will beprotected from overheating in view of the heat being drawn from thecentral portion of the heat exchanger 51. Another effect is that a readysupply of hot water will be available thereby decreasing the time lag toreceive hot water, if the closed loop circuit 701 is in operation, thatis, if the central heating option is in use.

[0216] If the central heating option were to be not in use, the circuit701 can be used to assist in the transferral of heat to the open loopcircuit 703 thereby providing water at a relatively high flow rate butalso, it is expected, to be with less thermal lag than by comparisonwith prior art systems.

[0217] Illustrated in FIG. 43 is a circuit very similar to thatillustrated in FIG. 42 and like parts have been like numbered. It isexpected that the embodiment of FIG. 43 will be able to provide hotwater with less thermal lag than prior art systems. In this embodimentthe heat exchanger 51 heats the cold water in the first instance. Theheat exchanger 51 is in a series connection with passages 717 of heatexchanger 716, which is the potable water side of heat exchanger 716.

[0218] In the situation where water (containing glycol) passes throughthe passages 717A of heat exchanger 716 is cooler than the water passingthrough passages 717, a bypass capability is provided by the openingand/or closing of valves 717B and/or 717C so that the bypass line 718Acan connect directly from the start of conduit 713 to the hot wateroutlet.

[0219] The same circuit can be used to ensure that the water jacketassembly 50 can be used not only as a hot water supply but also aheating mechanism whereby the closed circuit is used to feed a series ofradiators positioned around a dwelling for the purpose of central roomheating.

[0220]FIGS. 41 and 41A illustrate the profiles of a plate 550A and 550Bto construct a water jacket assembly that can be used in the FIG. 42 or43 dual circuit approach. The end plates 550B are of a similarconstruction to the plates 560 of FIG. 35. The panel has four apertures795, 796, 797, 798 to form 4 headers, and are arranged vertically and inline centrally of the panel. The lower aperture 795 is the first waterheating line (equivalent to item 703A of FIG. 42), the next aperture 796constitutes the cold water input (equal to item 711 in FIG. 42). Thesecond water heating line which is the closed circuit is illustrated asthe aperture 797 connects to 701B of FIG. 42 and the hot water outletaperture 798 is the third highest aperture and connects to 701A of FIG.42.

[0221] Whilst the plate 550A of FIG. 41 only has inlets and outlets fortwo circuits illustrated, it will be readily understood that additionaloutlets and inlets can be provided on the heat exchanger plates and heatexchanger formed therefrom so that other water circuits can beconnected. By this means hot water for a variety of purposessimultaneously is capable of being produced at relatively low cost as aresult of the means of construction of the water jacket assembly.

[0222] Illustrated in FIGS. 44 to 46 is a water heater 10B similar inconstruction to that of FIGS. 31 to 33 and like parts have been likenumbered and their function and purpose need not be described further asreference can be made to earlier description. The difference betweenthese two embodiments is that the plates 550B and 560B even though stillof a generally Y and T shape are configured and arranged so as to beparallel to the width of the water heater 10B. This configurationresults in the use of a lesser number of actual plates albeit biggerones but this is helpful for dimensional stability and integrity of thewater jacket assembly when in use. In FIG. 44 the flow path through thewater jacket assembly 50B is illustrated. In FIG. 44 it can be seen thatthe two flow paths are the mirror image of each other.

[0223] Illustrated in FIGS. 47 to 49 is a further embodiment of theinvention. FIG. 47 is a front elevation of a water heater 10C having awater jacket assembly 50C, which differs from water jacket assemblies50A and 50B of previous Figures.

[0224] Illustrated in FIGS. 49A and 49B are the five component platesand the four plates assembled from the component plates, which whenpaired form heat exchanger elements, which when sandwiched form waterjacket assembly 50C having combustion chamber 50A, a heat exchanger anda water jacket.

[0225] A first plate is end plate 380A which effectively forms the endsor side portions of each of the plates illustrated in FIG. 49 inexploded view. The second plate is 380D from which plates 380B and 380Eare formed by the punching of an aperture therethrough. The third plateis 380C.

[0226] The burner plate 380 is made from two end plates 380A and acentral plate 380B. The plate 380B has a central circular aperture 381therein. As the view in FIG. 49 is from the top, the underside is notvisible. However, once plates 380A has been joined to 380B they form asingle plate which can be joined to a like plate (not illustrated)having a nesting flange similar to the flange 600 (but in the oppositedirection relative to the dimple formations) such that the dimples onthe surfaces of the back to back plates join together to form channelsbetween the respective plates. In this way, a single heat exchangerelement can be formed. Further, if desired, the plate 380A can be of adifferent metal to the plate 380B to take account of heat resistance ofthe metals used if such a requirement is necessary.

[0227] The aperture 381 through the plate 380 will form a through holein the corresponding heat exchanger whereby this element is used as theupper most element in the water jacket assembly 50C. This element in usehas a fan shroud 382 passing through the aperture 381 and sealstherewith as illustrated in FIGS. 47 and 48. The burner 20 asillustrated in FIG. 47 is attached to the shroud 382 and is of acircular type that can radiate flame 360° therearound, or alternativelythe burner 20 will send flame to the left and right sides of combustionchamber 50A.

[0228] The plates 383 which form the combustion chamber 50A areconstructed in a similar manner to the plate 380 except that the plate380B is replaced by a channel plate 380C, with each plate 383 having twoof these. The channel plates 380C conduct water from the left end plate380A over to the right end plate 380A on plate 383. A stack of pairs ofplates 383 form heat exchanger elements, as indicated in FIG. 47 betweenthe top plate 380 and a separation plate 390.

[0229] Two of the separation plates 390 form an end heat exchangerelement for the combustion chamber 50A. This end heat exchanger elementis constructed from two plates made up of end plates 380A and a centralplate 380D which in the central portion thereof has a flat closedsection. If desired, the plate 380D could have a series of dimplesacross the flat closed section for the purpose of forming a channelthrough the central portion of the plate 380D. However, as this wouldincrease the number of plates required, this may have an undesirableeffect of increasing the overall cost to manufacture a water jacketassembly 50C.

[0230] The plates 392 form flue elements (so described because theyprovide therein a flue by which the combustion products may escape). Theplates 392 are made from two end plates 380A and a central plate 380E,which has an aperture 381A, which is preferably larger than aperture 381of plate 380.

[0231] Most plates 380A have an aperture 232A, which when adjacentplates are positioned back to back to form elements and the elements aresandwiched to form the water jacket assembly 50C, will form a left andright side header 390A and 390B when all plates and elements areassembled. It will be noted that the plate 380 has its right sideaperture 232A blanked off so that water will not pass through the uppermost plate 380. Similarly the lower most plate 392 is also blanked offto prevent water passing therethrough. The right side header 390B isthus formed between the uppermost plate 380 and lower most plate 392. Itwill be noted that plate 390 is blanked on the left side thereof so asto divide the left side header 390A into an upper and lower chamber, thepurpose of which will be described below.

[0232] It will be noted that all but the uppermost and lowermost of theend plates 380A have two apertures 388 thereon. These apertures 388provide a passage 388A for the combustion products to move outwardlyacross the heat exchangers from the centre as illustrated in FIG. 48 andout to the left and right sides. All the apertures 388 together andaligned form a left and right hand side downward passage as illustratedin FIG. 48 whereby the exhaust gases will move past the separation plate390 and then begin an inwardly directed motion across the flue plates392 passing out of the central aperture 381A and out of the flue 381Bwhich is formed at the base of the heat water jacket assembly 50C.

[0233]FIG. 47 illustrates the water flow path through the heat exchangerelements which make up the water jacket assembly 50A, while FIG. 48illustrates the hot combustion gas flow path . The left and rightheaders 390 A and 390B and left and right side vertically orientedcombustion paths 388A cannot be viewed easily from a single frontelevation as they are located one in front of the other as FIGS. 49A and49B illustrate.

[0234] While the above illustrates and describes the plates 380, 383,390 and 392 as being an assembly of plates, they could each be made froma single integral plate.

[0235] As can be seen from FIG. 47 the direction of the liquid flow pathis upward from the cold water supply to fill a lower portion of leftside header 390A. Once lower portion of header 390A is pressurised waterflows from the left to right, across the flue plates 392, then up intoright side header 390B. From header 390B the water travels from theright hand side of the plates 383, 390 and 380 into the upper portion ofleft side header 390A. The upper portion is a separate chamber to thelower portion in the region of the flue plates 392 with the hot waterexiting at exit 15 as in the previous embodiments. A typical water flowpath such as formed in elements formed by plates 392 is schematicallyshown at the bottom of FIG. 49.

[0236] As can be seen the shape of the path is zig-zag (and helical) asin the previously described embodiments. The zig-zag/helical pathtravels across half the depth and ultimately across the full width ofthe plates in a serpentine fashion. The difference with the heatexchangers formed by plate 383 is that the channel plate 380C has astraight line flow path straight across from the left hand side plate380.

[0237] The water jacket assembly 50C differs in that it is made up of 5plates which are oriented in a generally horizontal arrangement. The topmost plate as illustrated in FIG. 37 substantially fully closed exceptfor a circular aperture 381 in the middle thereof. Two such plates areplaced back to back to form the upper element through which the fanshroud 382 passes and seals therewith. The burner 20 in this instance,is attached to the shroud 382, and is' of a circular type that willradiate flame in 360 degrees therearound. The combustion products, underthe influence of the fan travel outwardly across heat exchangers formedfrom plates 384 as illustrated in FIG. 48. The plates 384 have arelatively large cavity 386 which provides the formation of thecombustion chamber 50A when several elements are stacked on top of eachother.

[0238] The combustion products move outwardly until the downward exhaustpassages 388A are reached. Then the passages 388A take the combustionproducts downwardly through the water jacket assembly until the middleheat exchanger 390 has been passed. This ensures that all combustionproducts must exhaust form the combustion chamber in a horizontaldirection.

[0239] Once past the element 390 has been passed, the combustionproducts can then travel between the heat exchanger elements 392 in theportion of the water jacket assembly below element 390.

[0240] The water flow path is illustrated in FIG. 36 and flows from theleft hand side of the water jacket assembly 50C to the right hand side.The channel or water path formed by the dimples in the plates 381, 392,390 and 384 has a continuous path around each element and a zig zag orsinusoidal path through the middle of the plate. The zig zag orsinusoidal path crosses the elements in a serpentine manner doublingback across the elements to increase the efficiency thereof.

[0241] Illustrated in FIG. 50 is a water heater having a storage vesselor accumulator 450 to receive hot water once a hot water tap has beenclosed. The accumulator 450 is of a generally circular construction butcan be any appropriate shape. The accumulator 450 receives hot waterfrom the water heater by suitable control systems and valves provided inthe heater. This hot water, once the hot water is closed, wouldotherwise remain in the water jacket assemblies described above.

[0242] Diverting the hot water to accumulator 450 ensures that stagnanthot water, which is prone to scale because of the risk of thetemperature increasing, will not remain in the water jacket assembly.The accumulator 450 is able to be used as a storage of hot water tominimise the lag time to deliver hot water to the hot water tap. In somecountries this lag time has to be minimised so as to preserve water.

[0243] The accumulator 450 has a flexible membrane 451, whereby hotwater is received in the chamber 452 on the water heater side ofmembrane 451 whereas the chamber 453 will have air therein or will ventto atmosphere allowing the membrane 451 to minimise the volume ofchamber 453 when hot water fills chamber 452.

[0244] The accumulator need only be of a volume sufficient to hold allthe hot water in the water jacket assembly with a 10% to 15% extravolume as a safety factor.

[0245] Illustrated in FIG. 51 is a schematic representation of a heatexchanger 430 made up of elements 431 formed from plates 432 which canbe like any of the previously described embodiments. The heat exchange430 is made from a series of adjacent elements 431 made from plates 432which are preferably identical but need not necessarily be so.

[0246] The improvement in FIG. 51 is the provision of a leading edgeplate 433 which is joined to what would have been the leading edges 434of elements 431. The joining can be by fusing, soldering, bronzing,welding or any appropriate means which provides good surface contact forheat transfer purposes between plates 433 and plates 432.

[0247] The leading edge plates 433 are manufactured from a metal havinghigh temperature resistance qualities such as appropriate stainlesssteel or titanium and/or its appropriate alloys.

[0248] The leading edges 435 of the plates 433 are at right angles toeach other. The leading edges 435 are angled in this way to support thecombustion process preventing quenching of the heat coming from thecombustion chamber which would normally tend to denigrate the combustionprocess. Notwithstanding this, the shape of the leading edges of theplates 433 can be any appropriate shape to protect the plate 433 in thisarrangement and to help support the combustion process. The leadingedges 435 and plates 433 can help to reduce CO₂ emissions from thecombustion chamber by helping to maintain heat therein to support thecombustion process.

[0249] In FIG. 52 is a heat exchanger with the flow path shown, forillustration purposes only, such as it would be if the plates weremanufactured from perspex or some clear material. The shape of the plateis of a Y configuration similar to some of the previous embodiments andthe flow path is formed in much the same way and has much the samecharacteristics. The plate of FIG. 52 and the heat exchanger formedtherefrom has a difference with the elements of previous embodiments inthat at two points in the flow path an opportunity for crossing over isprovided. These cross overs are at points 527A and 527B. In the flowpath water travels from the lower header 233, out to the left and righthand sides thereof, then upwardly and back towards the centre toapproach the first cross over at 527B. Depending upon water pressure andother physical characteristics the two flows may either cross over eachother; pass through each other; or generally fill the central dimples ofthe cross over and then from there radiate outwardly in the right andleft hand direction. It is possible that the water may not actuallycross over but rather may keep to the respective halves of the plate.

[0250] After passing the first cross over 527B water will radiatetowards the left and right sides then up around the outside then up thearms 552 and 553 of the Y shape back, then down towards the centralportion of the plate. The path then approaches the cross over 327A fromthe left and right sides.

[0251] At cross over 527A, again, depending upon physicalcharacteristics the water may or may not cross over; may or may not passover; under or through. However water will continue to flow from thecentral dimples of the cross over in an outward direction along thepredefined paths making its way back along the leading edge into theupper header 232.

[0252] In this embodiment it can be seen that the leading edge 260 hasan appropriately scalloped or shaped leading edge so that the materialof the leading edge is such that along any point thereon the distance tothe closest channel or dimple is roughly the same across the same of thewhole leading edge. This ensures that hot spots which might otherwisehave formed because of being a further distance away from the channel ordimples will not be created.

[0253] The construction and flow path illustrated in FIG. 52 is thoughtto be advantageous in that if any one portion of the flow path were tobe effected by scale, water could still flow through at least half thecombustion chamber.

[0254] Illustrated in FIG. 53 is an end heat exchanger which could beutilised with the embodiment of FIG. 52. Whilst there are no cross oversin this element and it is constructed in a similar manner to the plate560 of FIG. 35 (and like numbers have been used for like parts). Aspecial feature of the plate of FIG. 53 is that a bypass passage 529A isprovided between the lower header 233 and the upper header 232. The useof such a bypass passage can be advantageous in that a lesser pressuredrop can be sustained.

[0255] Illustrated in FIG. 54 is a water heater 10D which uses a waterjacket assembly 50D similar to water jacket assembly 50B of FIGS. 44 to47. Like parts have been like numbered and their function and purposeneed not be described further as reference can be made to earlierdescription.

[0256] The difference between the water heater 10D and 10B of FIGS. 44to 47, is that he water jacket assembly 50D is utilised with a burner 20which is naturally aspirated and is oriented so that the combustionproducts flow in an upward direction. As can be seen in FIG. 54, thewater jacket assembly 50D is rotated through 180 degrees by comparisonto water jacker assembly 50B of FIGS. 44 to 47.

[0257] Each of the embodiments previously described above do or can usea cold water bypass which helps to increase the pressure at the outputas well as to control temperature. By providing electronicallyadjustable valves on such bypasses (although no valve is envisaged forthe bypass 529A of FIG. 53) the bypass can be adjustable to cope withconditions as sensed by the control unit 80 which may need to increaseor decrease the flow through the bypass thereby achieving both hot waterand a higher pressure at output.

[0258] One of the features of the water heaters of the present inventionis that several prior art instantaneous water heaters tend to have aserially connected water passage through the heat exchanger. One of thedistinct advantages of the present invention is the ability to “gang up”or “connect in parallel” heat exchanger elements made up of similarlyshaped plates which can result in a lower pressure drop from the inletto the outlet of the heat exchanger in view of many parallel flowsoccurring simultaneously through the heat exchanger elements.

[0259] The above description and method of manufacturing a heatexchanger, water jacket and combustion chamber assembly is such that oneof the advantages is that the construction and features allow for amodular and scalable unit. The term scalable is used in the sense ofbeing able to scale the size up or down according to the amount of MegaJoules utilised or required from the hot water system. For example, in ahot water system that would utilise approximately 200 Mega Joules ofenergy per hour, the combustion chamber/water jacket/heater exchangerassembly of FIG. 37 which will have effectively two end elements andthree heat exchanger elements would be of a size generally suitable forexample for say 60 to 90 Mega Joules of heat throughput. To increasethis to a 200 Mega Joule unit some twelve heat exchanger elements madeup of some 24 plates would be utilised for the heat exchanger portionand four plates to form two end heat exchanger elements to encase andform the combustion chamber and ends could be provided. Of course, aburner size would have to be increased to allow for the greater widthand to ensure that combustion flow passes across the whole width of theheat exchanger portion or the combustion chamber width.

[0260] It will be readily understood that while the description of theabove embodiments is generally directed to an externally mounted,domestic gas fired instantaneous, fully condensing, fan forceddownwardly drafted water heater, that the inventions described hereinare applicable not only to this specific type of water heater but alsoto instantaneous water heaters that may have different characteristicssuch as:

[0261] naturally aspirated or natural draft burner systems

[0262] systems which can be mounted or located either internally orexternally of a building

[0263] with or without fully condensing heat exchanger operation

[0264] commercial, industrial or domestic systems

[0265] orientation of combustion chamber and combustion gas flow pathcan be in any one of the following directions: upwardly; downwardly;side ways directed; directed at an angle to the horizontal and orvertical.

[0266] While the above descriptions of the embodiments generallyutilises identical plates to form heat exchanger elements, it will alsobe understood that non identical plates can be utilised. By the use ofnon identical plates different shaped flow paths can be produced tothose described above which in the main tend to be somewhat regular andin some cases symmetrical in front elevation. However, to produce a flowpath such as a saw tooth shape made up of one vertical path lengthconnected by an angled path length, will require the use of nonidentical plates if dimples are to be formed on both plates. Clearly, ifa flow path is formed from a plate having a continuous channel thereinand is joined to a flat plate, the shape of the path of the continuouschannel can be any desired shape.

[0267] It will be understood that the invention disclosed and definedherein extends to all alternative combinations of two or more of theindividual features mentioned or evident from the text or drawings. Allof these different combinations constitute various alternative aspectsof the invention.

[0268] The foregoing describes embodiments of the present invention andmodifications, obvious to those skilled in the art can be made thereto,without departing from the scope of the present invention.

[0269] For example fusing is the preferred process described above tojoin and hold plates and adjacent plates together. This can besubstituted by any joining or holding process such as suitableadhesives, mechanical clamping systems with appropriate sealingmechanisms; welding etc.

1. A water heating system to heat water with combustion products, saidsystem including at least one heat exchanger element being formed fromfirst and second plates joined together to form at least one channeltherebetween to provide at least one liquid flow path between an inletand an outlet, said flow path being inside of said element and acombustion products heat transfer surface on the outside thereof, saidelement being characterised by said at least one flow path eachconsisting of a single path which extends across a portion of saidelement away from said inlet in one direction and across said portion inthe opposite direction toward said inlet, in a serpentine manner.
 2. Awater heating system as claimed in claim 1, wherein said flow pathextends across the full width of said element.
 3. A water heating systemas claimed in claim 1, wherein said flow path extends across said platein a zig zag or sinusoidal configuration.
 4. A water heating system asclaimed in claim 1, wherein said first plate has a single continuousgroove whereby when a flat second plate is joined thereto, said channelis formed.
 5. A water heating system as claimed in claim 1, wherein saidfirst and second plates each have a series of discrete dimples therein,whereby adjacent dimples on said first plate are connected by the seriesof adjacent and partially overlapping dimples on said second plate toform said channel.
 6. A water heating system as claimed in claim 1,wherein said serpentine manner is such that the flow crosses the elementat least twice.
 7. A water heating system as claimed in claim 1, whereinsaid water flow path is shaped like one of the following: generallyhelical; cork screw; square helical; or vortex shaped.
 8. A waterheating system as claimed in claim 5, wherein said flow path requiresliquid flowing therein to travel along one of said dimples in said firstplate having a straight line pathway then flow through an approximately90° direction change into said second plate then through anapproximately 90° direction change to flow through an adjacent dimple insaid second plate in a straight line pathway through said adjacentdimple.
 9. A water heating system as claimed in claim 5, wherein saiddimples provide a straight line path after transition from said firstplate to said second plate whereby the maximum length of the straightline path is in the range of three to seven times the depth or height ofthe dimple.
 10. A water heating system as claimed in claim 1, whereinsaid first and second plates each have a flared end extending away froma joining plane of said first and second plates.
 11. A water heatingsystem as claimed in claim 10, wherein said flared ends extend along theside edges of said plate from a leading edge to a trailing edge.
 12. Awater heating system as claimed in claim 10, wherein said flared endsextend for a distance in the direction towards the centre of said platealong leading and trailing edges.
 13. A water heating system as claimedin claim 1, wherein said element is formed from identical plates placedback to back.
 14. A water heating system as claimed in claim 1, whereinsaid heat exchanger and or plates forming said heat exchanger have anestable shape.
 15. A water heating system as claimed in claim 1,wherein said heat exchanger element has a shape which includes a mainportion and at least two arms extending away from the main portion. 16.A water heating system as claimed in claim 15, wherein the two armsextend in the one of the following directions away from the mainportion: parallel to each other; diverging away from each other;converging towards each other; or produces any one of the followingshapes: as a Y shape, U shape, C shape, E shape H shape, V shape or anyother appropriate shape
 17. A water heating system as claimed in claim16, wherein the arms of the element when placed near to adjacentelements form a water jacket around a combustion chamber.
 18. A waterheating system as claimed in claim 15, wherein said heat exchangerelement has a shape whereby the two arms extend in opposite directionsto each other, such as in a T shape.
 19. A water heating system asclaimed in claim 18, wherein the cross bar of said T shape forms an endwall of said combustion chamber.
 20. A water heating system as claimedin claim 1, wherein said element includes at least one dimple formationthereon whereby when two or more of such elements are position side byside, said dimple formations are aligned to form a header which canreceive a liquid and which will direct said liquid through each of saidheat exchanger elements simultaneously.
 21. A water heating system asclaimed in claim 1, wherein the leading edge is profiled tosubstantially follow the flow path.
 22. A water heating system asclaimed in claim 21, wherein points along said leading edge have aminimum distance to the nearest channel such that said minimum distancesare similar.
 23. A water heater system as claimed in claim 1, whereinsaid plates each have a formation to allow all plates to be restedtogether prior to fusing.
 24. A water heating system as claimed in claim23, wherein said formation is a flange on said first and second platessuch that when placed back to back said flanges all extend in the samegeneral direction.
 25. A water heating system as claimed in claim 24,wherein said flange is at an angle to said plate.
 26. A water heatingsystem as claimed in claim 24, wherein said flange extends partiallyaround the periphery of said plates.
 27. A water heating system asclaimed in claim 24, wherein said flange extends wholly around theperiphery of said plates.
 28. A water heating system to heat water withcombustion products, said system including at least one heat exchangeelement being formed from a first plate and a second plate forming achannel therebetween to form a liquid flow path inside of said heatexchanger and a heat transfer surface on the outside of said heatexchanger wherein the configuration of said liquid flow path and thussaid heat transfer surface varies across the width of said heat exchangeelement in one or more of the following characteristics: the crosssectional area of the liquid flow path; the angle at which the liquidflow path lies to the leading edge; the length of said liquid flow path;the amount of resistance to liquid flowing in said liquid flow path; theamount of resistance to combustion product passing over the heattransfer surface.
 29. A water heating system as claimed in claim 28,wherein said first plate has a single continuous groove whereby when aflat second plate is joined thereto said flow path is formed.
 30. Awater heating system as claimed in claim 28, wherein said first andsecond plate each have a series of discrete dimples whereby adjacentdimples on said first plate are connected by dimples on said secondplate to form said liquid flow path.
 31. A water heating system asclaimed in claim 28, wherein said flow path is of one of the following:a zig zag configuration or a sinusoidal configuration.
 32. A waterheating system as claimed in claim 28, wherein said flow path isconfigured to provide at or near to a leading edge of said element, adifferent length of straight line sections compared with the length ofstraight line section in the vicinity of a trailing edge of saidelement.
 33. A water heating system as claimed in claim 28, wherein saidflow path has a single path which extends across all or part of saidelement in a serpentine manner.
 34. A water heating system as claimedclaim 28, wherein said flow path extends across part or all of saidelement at least two times.
 35. A water heating system as claimed inclaim 28, wherein the included angle between lengths of dimples orsegments of channels on said first and/or second plate in the vicinityof a leading edge is varied by comparison to the included angle in theregion of a trailing edge.
 36. A water heating system as claimed inclaim 31, wherein the amplitude of said zig zag or sinusoidalconfiguration is varied in said flow path in the vicinity of saidleading edge by comparison to the amplitude of said zig zag orsinusoidal configuration in the vicinity of said trailing edge.
 37. Awater heating system as claimed in claim 28, wherein said flow pathdivides into a multiple number of parallel liquid flow paths connectinga channel across said elements in the vicinity of said trailing edge toa channel across said elements in the vicinity of said leading edge. 38.A water heating system as claimed in claim 1, wherein the thickness ofsaid heat exchanger element increases from said leading edge to saidtrailing edge.
 39. A water heating system as claimed in claim 1, whereinthe depth of said dimples on said plate or plates increases from saidleading edge to said trailing edge.
 40. A water heating system asclaimed in claim 38, wherein when two or more elements are positionedadjacent to each other a combustion products' flow path is formedbetween adjacent plates, said combustion products' flow path, near tosaid leading edges being of a different cross sectional area than atsaid trailing edges.
 41. A water heating system as claimed in claim 1,wherein the element is formed from plates made from two or more platesegments which are bonded together to form a composite single plate. 42.A water heating system as claimed in claim 41, wherein said plate canhave segments are made from different materials.
 43. A water heatersystem as claimed in claim 1, wherein said heat exchange elements have aleading edge formed of a different material to the rest of the heatexchange element which contains said dimples or channels.
 44. A waterheating system as claimed in claim 43, wherein said leading edges have ashape or result in the effect of promoting combustion in the combustionchamber.
 45. A water heating system as claimed in claim 1, wherein saidheat exchanger element includes a by pass channel which connects anentry header to an exit header.
 46. A water heating system as claimed inclaim 1, wherein the water flow paths in said heat exchanger elementcross over each other at predetermined points to enable water flowingtherein to mix with, pass through, or pass over and under, each other.47. A water heating system as claimed in claim 1, wherein said waterheater heat exchanger element has more than one inlet and one outlet,with each inlet having communication to one outlet, so that said heatexchanger element can have more than one liquid circuit passingtherethrough.
 48. A water heating system as claimed in claim 47, whereinwhen in use the hottest parts of the heat exchanger element receives afirst circuit, while a second circuit is heated in a cooler part of theelement.
 49. A water heating system as claimed in claim 1, wherein saidwater heater heat exchange element has in addition to a series ofdiscrete dimples, a continuous peripheral path to serve a water jacketfunction.
 50. A water heating system as claimed in claim 1, whereinthere are a plurality of said elements which are like oriented in saidheat exchanger and placed in parallel.
 51. A water heating system asclaimed in claim 50, wherein the outside surfaces of dimples of saidfirst plate of one element make contact with outside surfaces of dimpleson said second plate at discrete lines or points of contact.
 52. A waterheating system as claimed in claim 51, wherein said discrete lines orpoints of contact are one of the following: held; joined; joined byfusion; joined by brazing; joined by soldering; joined by diffusionbonding.
 53. A water heating system as claimed in claim 52, wherein inuse, combustion products are forced around said channels and saiddiscrete lines or points of contact forming a multi convolutedcombustion path through said heat exchanger.
 54. A water heating systemto heat water with combustion products, said system including plateshaving therein an array of dimples, said plates being placed together inpairs, the pairs of plates being arranged in parallel to form a heatexchanger, the heat exchanger being bordered by a water jacket beingformed from plates having therein channels or dimples to allow water toflow through said jacket, said jacket being joined to or integral withthe heat exchanger, said heat exchanger and water jacket having passagesinterconnecting them to allow liquid to pass therebetween, the assemblybeing held together to define a combustion chamber with combustionproduct passages and water passages within said assembly.
 55. A waterheating system as claimed in claim 54, being formed from a plurality ofplates including at least a first plate for forming a first heatexchanger element and at least a second plate for forming a second heatexchanger element whereby each of said plurality of first plates arejoined back to back with like plates to form a plurality of intermediateheat exchanger elements and each of said plurality of second plates arejoined back to back with like plates to form a plurality of end heatexchanger elements, said heat exchanger assembly being constructed bysandwiching said intermediate heat exchanger elements between said endheat exchanger elements and holding them together.
 56. A water heatingsystem as claimed in claim 54, wherein said elements are generallyvertically oriented so that when said elements are assembled leadingedges of said elements are generally aligned with the depth of saidwater jacket assembly.
 57. A water heating system as claimed in claim54, wherein said elements are generally vertically oriented so that whensaid elements are assembled the leading edges of said elements aregenerally aligned with the width of said water jacket assembly.
 58. Awater heating system as claimed in claim 54, wherein said elements aregenerally horizontally oriented.
 59. A water heating system as claimedin claim 58 wherein said elements include apertures therethrough topermit combustion products to flow between pairs of elements.
 60. Awater heating system as claimed in claim 54, wherein the plates of theheat exchanger are adapted to cause turbulent flow of water through thewater passages.
 61. A water heating system as claimed in claim 54,wherein the plates of the heat exchanger are adapted to cause turbulentflow of combusted gases past the exterior.
 62. A water heating system asclaimed in claim 54, wherein the plates of the heat exchanger are suchthat their exterior surfaces also provide an escape path for condensatethat forms in use.
 64. A water heating system as claimed in claim 1,further including a storage means to receive hot water which wouldotherwise remain in said apparatus when a user has closed a valvepreventing further hot water passing through said valve.
 65. A waterheating system as claimed in claim 64, wherein hot water in said storagemeans is passed through said valve once said valve is re-opened.
 66. Awater heating system as claimed in claim 28, further including a storagemeans to receive hot water which would otherwise remain in saidapparatus when a user has closed a valve preventing further hot waterpassing through said valve.
 67. A water heating system as claimed inclaim 66, wherein hot water in said storage means is passed through saidvalve once said valve is re-opened.
 68. A water heating system asclaimed in claim 54, further including a storage means to receive hotwater which would otherwise remain in said apparatus when a user hasclosed a valve preventing further hot water passing through said valve.69. A water heating system as claimed in claim 68, wherein hot water insaid storage means is passed through said valve once said valve isre-opened.
 70. A water heater system having at least two water flowpaths, with both paths passing through a water/gas heat exchanger, whichtransfers heat from combustion products to water contained in saidcircuits, a first of said at least two paths including a serialconnection to a radiator means and a serial connection to a water/waterheat exchanger where water in said first path can transfer heat to orreceive heat from water in said second path.
 71. A water heater systemas claimed in claim 70, wherein said water in said first path is in aclosed loop.
 72. A water heater system as claimed in claim 70, whereinsaid second of said at least two paths includes a cold water inlet. 73.A water heater system as claimed in claim 70, wherein said cold waterinlet is split into two water flow sub-paths, a first sub-path todeliver water to said water/water heat exchanger and a second sub-pathto deliver water said water/gas heat exchanger.
 74. A water heatersystem as claimed in claim 70, wherein said second sub-path can mergewith said first sub path for water to flow out of said system, when avalve on an outlet conduit from said system is in an open condition. 75.A water heater system as claimed in claim 73, wherein when a valve on anoutlet conduit from said system is in a closed condition water in saidfirst and second sub-paths is circulated.
 76. A method of manufacturinga heat exchanger assembly including making profiled heat exchangerplates, placing pairs of plates together to form a heat exchangerelement, placing a plurality of heat exchanger plate elements togetherto form a sandwich, said assembly having a combustion chamber andcombustion products passages and water passages within said assembly andwherein two type of heat exchanger elements are formed, end elements andintermediate elements with said end elements having a different waterpath to said intermediate elements.
 77. A method as claimed in claim 76,wherein said heat exchanger plates are manufactured such that thoseportions not required on a blank for one plate are a part of the nextsuccessive plate stamped.
 78. A method as claimed in claimed in claim76, wherein said heat exchanger elements can be assembled in parallel,which can be any one of the following: vertically oriented wherein theelements extend such that their leading edges run generally parallel tothe width of the water heater into which the heat exchanger assemblywill be installed; vertically oriented wherein the elements extend suchthat their leading edges run generally parallel to the depth of thewater heater into which the heat exchanger assembly will be installed;or horizontally oriented in the water heater into which the heatexchanger will be installed.
 79. A water heating system as claimed inclaim 28, wherein said water heater heat exchange element has inaddition to a series of discrete dimples, a continuous peripheral pathto serve a water jacket function.
 80. A water heating system as claimedin claim 54, wherein said water heater heat exchange element has inaddition to a series of discrete dimples, a continuous peripheral pathto serve a water jacket function.